I am using an mBot mK 7 extruder
It is all metal, uses a heater (vs a resistor), has a good hobbed gear direct drive
from stepper motor, has fan to cool top section.
I switched from thermocouple to thermistor so I could directly plug it into RAMPS.
Bad situation was when using nylon, It blobbed up around hot end for an hour print
and I had to melt off the nylon (with a torch) and rebuild the entire hot end and
replace the thermistor. I still need to replace the 0.35mm nozzle which seems to be
partially clogged.
It works great with PLA and ABS.
I take it apart and put it back together a lot -- very easy disassembly / assembly
except for perhaps mounting on baseplate.
http://www.mbot3d.com/collections/toolh ... -mbot-cubeIt appears the newer ones use a plastic part around hobbed gear.
I have a QU-BD extruder in stock that I will also try out