I’ve owned and worked on a lot of different tape machines and formats, and the same goes for mixing consoles. I’ve also personally owned a pair of MG1212s.
First of all, to your last question about the differences between the MG1212 and the MG1214, I believe the MG1214 included improvements in the transport mechanism for reliability, an improved mic preamp, and there was something about the sync interface...
Here is why I bought the pair that I had for awhile...sheer curiosity. If you are looking to get something to actually use as your only tape machine, I think it’s not such a good idea for several reasons:
1. The transports are problematic and often need work, and the transports being more complicated (mainly resulting from the loading/unloading mechanism...these are, after all, patterned after video cassette type transports and use a proprietary cassette derived from the obsolete Sony Betamax Cassette format...*different* than Betamax...not compatible, but similar), so you can expect some headaches now or later with an Akai MG series machine; not impossible to fix and there are some very good threads right here in this forum about that.
2. The tapes...again, proprietary format cassette, hard to find, expensive when you do, nobody can verify what tape type was loaded in the shells from the factory, rumor has it the tape was similar to Maxell EE formulation, but, again, nobody knows for sure and I wasn’t even able to verify whether the tape was a 1mil or 1.5mil class tape. Some people buy new tape and reload the shells with new tape. This can be done, but again what tape type to reload so you are using the proper tape in the transport? Nobody knows. And if the reloaded tape is thicker than the factory tape how are you going to reset the tensions and all that...it’s getting harder and harder to find the proper equipment to do this, and IIRC the service manual was not clear about that sort of thing because they assume you are using factory cassettes...they didn’t assume you would be reloading the cassette shells with something that may or may not be consistent physically or magnetically with the factory tape.
3. Basic maintenance...calibrating a tape machine is a standard activity if you own one. You have to have a calibration tape set the playback level, and the rest of the steps depend on accurately setting the playback level. When is the last time you saw a set of cal tapes for an MG series machine? I used to own a set. I sold them. I doubt I will ever see a set again. Could you buy a short form 1/2” open reel cal tape, transfer the tape to an Akai MK20 shell and use it? Yes. Would it be the correct tape physically and have the correct fluxivity? Can’t tell you. Because they don’t reveal that spec in the owners or service manual. Why? Because they assumed you would use the factory tapes and factory cal tapes and so who needs to know the specs? It is probably 250 nWb/m, but I do not know for sure. Oh, and what about biasing the tape in your reloaded shells? The service manual is also not clear about that, because if you were doing what Akai intended, you were always using the factory mystery tape and would not need to bias for different tape formulations.
4. Poor user community support...there aren’t a lot of people operating MG series machines, and anymore being able to connect with lay-users for community support if you have a tape machine is now, and has been for some years, of critical value. So I think, if you are getting into multitrack tape, it’s best to buy a machine that has a wide base of user support, and is a more readily used format.
5. The mixer...you suggested maybe it’s worthwhile to buy an MG series machine just for the mixer alone. Here’s the problem with that...yes either the 1212 or 1214 will give you a 12x2 mixer, but the EQ section is 3-band peaking type filters on each band...they’re all swept bands but I find greater value in hi and lo shelving filters than peaking. So I don’t think the EQ is a draw. There are only 2 aux busses. Okay...so at least there’s 2, but this thing is relatively huge and really heavy. Couple that with the limited feature set and you have to ask “why would you do that to yourself” when you can find a better vintage console with WAY more features for the same or less money? Deal breaker: there are no direct outs, and no mix busses. This is a straight 12x2 console with 2 aux busses. There are some nice little features (switchable aux busses, one is pre/post, the other is tape/post...EQ section is switchable on/off...), but, again, if you want to use a 1212 or 1214 as a mixer only, you’ll have no way to get your 12 inputs out to your DAW or whatever...no direct outs. Yes each channel has separate insert send and receive jacks, and you could use the send as a direct out, but that is, I believe, pre fader, pre EQ...and here’s another thing, you’re probably going to have to exercise some TLC even if you want to use just the mixer. There’s a battery mounted to the power supply PCB that typically is leaking by now. That will have to be replaced and the PSU PCB possibly repaired due to the damage from leakage. And both of my 1212s had janky mixer sections. Like I’m sure they could be made to work, but it would require disassembly and cleaning contacts of the card edge connectors, possible reflowing of solder joints...the LED meters weren’t working right, intermittent signal connectivity etc. Oh I guess there are direct outs on each channel...but they only feed the corresponding tape track. I suppose it would be quite feasible to modify that signal path to feed jacks vs tape tracks, but you’d have to research that one...and *why* go to all that trouble...there is nothing particularly remarkable about the MG mixing section...not “bad” but nothing magical happening there. Lastly, these are lower headroom devices...the audio power rails are +/-12V vs the more typical +/-15V or even +/-17 or 18V. So it’s a pretty hard sell in my mind to pay $100-200 for a 12x2 mixer with no direct outs that weighs a ton and has a relatively huge footprint...and has relatively low headroom. None of this adds up for me.
Now, it seems like I think the MG series machine are just steaming piles of goo. No. I just think at this point in time they should be low on the list of considerations for someone either new to owning/using a multitrack tape machine, or looking to choose a sole multitrack tape machine for a working studio. These were nicely built machines, and for what they are have a really practical and robust feature set...there was nothing about the ones I owned that I thought was chintzy or cheap, they just have the odds stacked against them after all these decades simply because of the design. The heads are Akai’s GX glass heads which have long wear life. There is a fantastic onboard multipoint autolocator using track 13 (the locator track), and there is a separate sync track...these could be master or slave in a sync relationship. So you have all those sync and locate features and never have to sacrifice any of the 12 audio tape tracks...which are wider than the Tascam 388 and you have 4 more of them...same tape speed (2 speeds available, 3 3/4ips and 7.5ips)...onboard dbx noise reduction...I consider the MG series machines to be a more robust build than the Tascam 388 and to have a much more comprehensive feature set as far as the tape machine. I like the 388 mixer section better, but the Akai beneath the skin is a more professional build...better designed; a more “professional” machine. I can’t recall the details now but I believe there is indeed something of a decent change in the mic amp between the 1212 and the 1214. People actually tracked hits on MG machines, of course with a host of outboard gear and professional mastering resources, but Google that...Phil Collins, U2 and others actually used MG series machines for their multitrack masters on some projects. But ultimately it circles back around to my points above and I just think if you want a working machine or even just the mixer, it just doesn’t make sense. Unless you’re like me and you just couldn’t help yourself because you always wondered...had to get one to see how they were made. I’m strange like that.
Hope this helps. Not trying to rain on any parade if such exists...or be excessively pragmatic. At the end of the day if you read all that above and you just feel that tug, like that local 1212 is calling you, well maybe that’s your machine and with diligent efforts and reviewing the good work shared right here on this forum you too could get one working reliably. It’s totally doable, but you have to be patient and thorough.