The only other USB device that has users (that I know of) is the KFlop and from what I have read it sounds good.
Some people have had problems with noise and the Smoothstepper, think the majority are down to wiring practices than anything else though but it is definitely more susceptible to noise than the parallel port.
Not sure what you mean regards the backlash comp, I presume its handled in the plugin but cant say for sure, it does seem to work well in the tests I have done.
Hood