I have a Masterlink, and I find it to be an incredibly useful item in my room- and also for recording live-to-2 in the field. I like the ability to master, mung, crop, mix and match, and then reassemble and render *before* getting to the point of committing to a CD copy. The Masterlink's internal disk replaces the reel of 2-track tape with paper leader and good old blue splicing tape, at least in my ancient worldview.
Without question, you can probably do the same thing with plugins in 3 or 4 different software packages. Frankly, if you're used to Windows screwing with your music, this product probably isn't for you. The thing the Masterlink brings to dinosaurs like me is that it is a good, old fashioned 2-track *plus* a bunch of modern digital tweeks. I treat mine just like I did my (much lamented) old 2-track mastering deck. However, the Masterlink brings the ability to EQ, to normalize, and to generally polish things in way I would prefer not to have to do with tape: reorder song lists, screw with intros and outros, yadda yadda. Sweet. No razor blades.
Is it the only way to do this? No. You wanna do the whole deal in your preferred editing software package? Knock yourself out. I don't have time to learn how. For people like me who still think of a studio as having a multitrack tape deck over *here*, and a 2-track mastering tape deck over *there*, and no computers in the room, the Masterlink fulfills a very important function: it stripes two tracks right out of the box, allows simple editing, can offer leveling and normalization, and never (and I do mean never) experiences the Blue Screen Of Death with your project tracks. Data goes in, data comes out, everyone's happy.
If you don't like Alesis products for some reason, this box will never fulfill your needs. But it does have a very special place in my room, because I don't care who built it, and I have neither the time nor the patience to screw with software, plugins, and such dreck: I want to run 16 tracks through my board, mix to 2, stripe it, and ship it. Right freakin' *now*, with no unpleasant delays to sacrifice a live chicken to the gods of Windows to protect my data. In short: it fits fine in my Cretaceous, or perhaps Triassic, working style.
Your mileage may vary. However, speaking strictly as a fossil here, I credit the Masterlink with giving me enough momentum to get back into this art form after a decade away, and I'm not kidding. Between that and the Fostex D1624, I have a new life in recording.
Will it replace sending your product to a pro mastering suite? No. Nothing can replace the "second-set-of-ears" function that those companies provide. But it's the next best thing: used intelligently it can help you get your material into the best shape possible, and that may in fact be exactly good enough for you. It's certainly good enough for me, since nothing I contemplate producing is ever likely to see major label distribution...
Your mileage may vary. Hope that helps...