The M2 was my first 3D printer, that I purchased in 2015. I wanted something fool-proof, sturdy, and repairable if needed. To be honest, while learning how to do 3D printing, I gave this printer a beating and it never failed. Once I figured out all my user errors with 3D Simplify and design-for-printing in general, the printer produced excellent quality. Eventually I got to the point where I no longer needed any kind of adhesive on the plate (glue sticks, painter's tape, hair spray; I tried them all), I can print PLA to clean glass with out issue. For ABS, I use the slightest amount of juice.
I was so confident in the quality that I put the printer online at 3DHub and took orders from customers. I would not have done that if it produced crap. I also posted a few prints to Thingiverse that I was proud of. I have successfully printed several 8 to 10 hour-long print jobs.
I really like the option to print custom parts for it as needed. Leveling the table took a bit to get right, but it holds its placement well so you don't have to level constantly. All the parts are easily accessible. I got Ninja Flex caught up in the extruder gear the first time (that filament is very flexible and needs a little extra guidance to thread); I simply disassembled the head with the supplied tools, cleared out the gear, and put it back together to continue printing in minutes.