Funny thing, I wouldn't use it as a regular mic pre, yet I quite enjoy it for bass. I've used mine as a front end to warm up cold-sounding amps, as a level matcher, to buffer passive basses against the low (10K) input impedance of my Radial JDI, as a 1/4" to XLR adapter, as an active DI...
It's a great low-cost gadget to have in your gig bag.
There are a lot of negatives that can be said about it (low-voltage power supply, too cheap to be any good, doesn't do tube overdrive, tube is hard to replace when it dies, etc.), but I don't really care about what's under the hood. Even if the tube is just window dressing, it's a cool sounding little box, for very little cash.
As far as tube replacement goes, I've been using mine on and off for about 5 years, and it's still working fine on the original tube. Even if I broke it trying to replace the tube and had to buy a new one, it doesn't owe me anything, especially now that the Studio is down to about thirty bucks!
One caveat: I prefer the regular Tube MP, simply because the VU meter on the "Studio" goes nuts if you DI into a channel that has phantom power on it. Diming the needle with 48V doesn't seem to affect the tone, but it can't be doing anything good for the meter!