I have both a Tube MP and an MP20. I love them both, but they're totally different from each other. The MP20 is clean, super-squeaky clean, with a very clear, uncolored sound. I would definitely describe it (and, c'mon guys, I'm comparing it to a tube MP, not a great river or something that costs three or four times as much) as "transparent." For me, it is THE thing to use on acoustic guitars, etc.... Has amazing amounts of gain and headroom, and even the built-in instrument preamps sound frighteningly good - I frequently blow myself across the room because the instrument pres are so quiet that I have no idea how high I have everything turned up.
The only "drawback" of the MP20 IS how clean it is - if you're used to the throaty tube sound from a slightly overdriven tube MP, you might be disappointed in vocals through the MP20. It would totally depend on the style of music you're recording, whether you want a "dirty" tube sound or a "clean" class a sound. These two units really are night and day, and I find that I really need both extremes of sound - for instance, bass and acoustic guitars recorded through the MP20 combined with vocals through a hot-running tube mp... Those are the best sounds I've EVER recorded (granted, yeah, we're talking home hobby studio here, but still...).
The MP20 is really well-built, and I'd be surprised if I ever had any problems with it. Got mine for $400 from ebay, and have never regretted a penny of it. It's as close to a "high-end" mic pre as I'll ever get, and even though it's a light year away from sounding like a Manley or Great River, etc., it's still a light year above what most people have been recording through for most of their lives (ie., cassette 4-track built-in mic preamps, and the like). I'd say go for it, and they still hold a really good resale value if you decided you didn't want to keep it.
