The 788's an all-in-one, compact, digital 8 track recorder & mixer- Portastudio. The mixer is all digital, with 8 inputs, 7 input faders, a couple rows of buttons, and all functions controlled thru this small LCD display. The media is a hard disc, and it has an optional CD burner. The CD burner can be used as a raw data backup, and a CD mastering device. The 788 records about 1 hour & 50 minutes, and then needs to be dumped or backed up. The 788 is pretty powerful, but it's all digital, and probably not as easy to use as an analog style Portastudio. The inputs & outputs are OK for a new user, but probably not as good as what an experienced user wants.
The Porta02 is the low-end cassette tape 4 track Portastudio. The mixer has only 2 inputs, and it has 2 band EQ. It runs at normal cassette speed only. It plays back 4 tracks with a minimal mixer.
It really depends what you want, and how much money you want to spend. The 788 & CDR will be well over $1000, and the Porta02 will be about $170, and both have their relative value.
I think if you were going to get a cassette 4 track Portastudio, the extra money spent on a 424mkIII would be well worth it. The 424mkIII is the top of the line 4 track cassette Portastudio, and has much better features than the Porta02. Shop the sales. I've seen the 424 for about $400.
And, if you're going to get the 788, you may be fine, but you may be better off in the long run with a nice analog mixer, like a Mackie 1642, and a discrete 8 track, like an ADAT or DTRS tape. This route will cost more money, of course.
Also, there's the used market, for older 1/2" reel 8 track analog decks, 16 track reels, etc.
Besides basic design features and useability issues, the issue of digital vs analog boils down to one thing: TAPE HISS. Analog has it, digital doesn't.