I was seriously going to purchase the B9.1ut, especially since it is now selling for $300. But when I saw I could get the B2.1u for $150, it was a no-brainer to get the B2.1u instead. Not that the B9.1ut isn't a good value. It's just the B2.1u is a so much better value. Compared to the B2.1u, the B9.1ut has no drum machine (essential for practice), takes up a lot more space and weight, and cannot run on batteries. What do you get for the extra $150 that the B9.1ut costs? A LCD screen, more controls and buttons to directly edit things, more refinement in the settings (0-50 instead of 0-10), a tube, a fancier expression pedal controller, and an aux in. OK, maybe I'd be willing to pay $50 extra for that, but not double! The 2.1u has the same (but less refined) eq, compression, tuner, effects, and many of the same emulations, as well as the same processor, latency time, direct out, headphone monitor, A/D and D/A, noise reduction, and USB port. The B2.1u is definitely more bang for the buck.
