I'm no expert, but I've used some of the budget preamps mentioned.
The Tube MP is a solid bass DI, and on rock vocals I imagine it has its place. But it's a bit noisy and lo-fi compared to other options. Like the DMP-3. I actually use DMP-2 pres that are built into my Omni mixer thing... they are clean and clear. A big step over the Tube MP for most uses, IMHO.
I've not used the VTB-1 but by all accounts it's clean and you can dial is a bit of "tewb" distortion, if you're into that.
It's in a bit of another price league, but I use the Groove Tubes Brick for vocals and bass, and it's VERY nice. Doesn't have all the gain in the world, but adds a certain something I find very useful.
Between the Brick and the M-Audio pres, I find I have most bases covered.