I have used this for around 4 months now and it has been almost perfect. Easy to feed new filament and even without a geared stepper, using mk8 I have plenty of torque. Never a problem with regular filaments.
The only down side, and this is common for any bowden it seems, is that it doesn't work 100% with flexible filament. I use a simi-flex that is not as flexible as ninjaflex, its more like oxygen tubing. But it will still pop out and get jammed enough that it cant print about half the time.
If the top hole was brought a little lower or if it had a little more support around it I think it might do the trick.
That being said. Tempo, if you could make this work better with flexible filament this just might be the perfect extruder, and I have tried a bunch.