I had one. I had two actually. Sold one. Still have one actually. Might or might not get rid of it.
The general rumor on it is that the phantom power is under powered. Not that I can verify that, but my Avenson STO-2's sound way different between using the Mobile Pre and
the Korg MR-1000 I currently use.
As far as mics. I used an AT4033a on one on dot 2 of 27 for a small-ish but loud brass ensemble. Decent, but from an EQ perspective, a little whacky. On dot 7 of 27 for a giant squid omni electret mics with 9V battery box. Not a desireable sound either. On dot 6 of 27 for my phantom powered STO-2's. Best so far, but a bit of a distance roll off and a little lacking on the low end for EQ.
Plenty of gain on the mobile pre. But the 16 bit @ 48kHz has a bit of a distance rolloff that I don't seem to have on the Korg at 24 bit. Still decent for the money, I guess. Certainly not the best of the best though. But useable.