I found brand-new kapton didn't hold anything very well, and suspect its too smooth initially, but after a couple of prints the smoothness is gone and it holds better. Though it always held enough for the print to make progress, just sometimes I had problems with warping and the piece pulling away f...

Be aware the at the connectors are non-standard for 40mm fans, which will typically have PC hookup connectors on them (at least, from what I have seen)
If your current fan is dead, you can salvage the connector from that one though and do some re-soldering yourself.

I'm a big fan of Octoprint (on a raspi). Super fast to upload gcode to. Zero problems with it printing. You don't need network, or a PC running in order for it to keep printing happily. I have zero problems with it on wifi. You don't need any internet connectivity at all for it to print. Also, you d...

Interesting. The kit build instructions don't include anything about securing the wiring like that, but it is a good idea. I should try and do that on mine.
Do the pre-assembled M2's come like that ?

My guess would be that the walls printed as hollow, in which case spongy is expected. You should be able to double check what S3D did by exploring the preview. It might have been narrow enough that it didn't bother infilling whatever gap it had. Is there some kind of minimum-area-to-infill setting ?...

What is the sales pitch on the PTFE v4 ? I have the v3b that came on my M2, and have had zero problems with it (though admittedly only used PLA/ABS through it) so far. I'm always up for buying new gadgets, but haven't quite been able to understand what an upgrade will get me (at least for PTFE one -...

The defect is on the back part of the print, when looking at the front of the printer, right ? It is common with PLA and happens because the front cooling fan which is there to 'set' the PLA after it is extruded doesn't have quite as good airflow onto the back of the model as it does the front. I'm ...

I would suggest powering it off, and manually centering every axis (just approximately), then retry the zero'ing, and watch which way everything moves. They should all be moving toward the end-stops. If they are moving the wrong direction, then clicking when they reach the wrong end, it would indica...

Z-stop adjusting instructions are here: http://makergear.wikidot.com/m2-getting-started
I think there might also be a youtube video about it.
If you haven't adjusted it properly before, then this is absolutely the first thing you must do.

Also, first layer height is pretty important. You need to make sure the bed is nice and level, and the z-stop is set correctly. When the first layer is going down, you want to look and see if the first layer looks slightly 'smushed'. If it just looks like a round tube of plastic carefully sitting on...