Welcome to the SeeMeCNC Community

I definitely have a tiny bit of backlash in mine, but it doesn't seem to affect the print much if at all. I got this Kysan stepper: http://www.kysanelectronics.com/Product ... ordID=8688
from tridprinting.com

I run the current at 135 in the Repetier firmware (0.75A) And it has never skipped once. My steps per mm with the 8mm toothed pulley from tridprinting comes to 463.24, which works out very nicely. I might lower the microstepping slightly on the axis to bring it down some, and save some of the step limit for the motion axes.

You really don't care about backlash on an extruder, it's really only ever driving one way, you might have to increase the retract settings to overcome any there is, and the backlash is usually relatively small.

The reason they are not commonly used is they are more expensive, and there are downsides to gearing steppers in general. The torque a stepper produces drops off with rpm, and they have relatively low max RPM's to start with, if you're trying to move something at reasonable speed adding a gearbox is going to hurt more than it helps.

None of that matters for an extruder, where speeds are low and your only really driving one way.