i'll agree that there are more things that could go wrong but i definitely disagree with the reliability..
running 5 UM3s compared to running 5 UM2s is a total breeze.. the UM3 is much more reliable in my experience..
What kind of issues do you have on the UM2 ?
issues I had.. i replaced them all with UM3.. ;-)
so i thought about it and i'm not going to list them :)most of them are solved with the UM2+..
for me, the biggest thing is the replaceable print heads.. any issue.. at all... heater, temp sensor, nozzle, heater block.. whatever.. replace it under a minute.. no downtime.. well worth it
I have no issues with 2+ but a lot with 3. When you replace the printcores, you always need to do the x/y calibration, it's a waste of time.