So I bought this little thing just because I took home a passive ribbon mic and according to what you read on many forums and blogs you need an external preamp to really get that thing making its magic.
At the same time I've been really impressed with the quality of the preamps built in my tascam us 16x08 and I wasn't so sure that such a cheap preamp could really take the sound to another level, so I ran a few tests on vocals, guitar, and bass guitar and found out that I was right.
The tube warmth feature doesn't really sound any good to me, at the beginning I thought that it was nice but I realized I was everytime going back to zero drive. I built a couple of tube amps for guitar, so I think to know how a tube overdrive device should sound, and this thing doesn't do it for me.
Compared to the Tascam's pre the PreSonus (used with gain knob at zero) offer a slighty different frequency response, I heard a bit more focus on the midrange which could help in recording midrange istruments like vocals, guitars, and maybe snare (didn't try that, just guessing) but for recording bass guitar I was happier with my audio interface's pres. Talking about audio clarity, this pre doesn't do anything more and anything less than my default pre.
So...if you have some really bad/old audio interface or just need an external pre to use a line level input this product could save your ass giving you a nice clear sound (don't drive it, just don't.) but in any other case I can't imagine how this pre could be helpful to you.