I agree with you Martin,
Idlers are cheap, and poorly fitted on mine too, i bought some new one and upgrade that part
i had two defective motor driver
the worst part i think is the bed melamine was not a good choice for such a critical part and the aluminum bed plate
needed more support so that it stay flat.
I have very good mechanical, electrical and electronics skills, so i was not afraid of diving into it.
i had to watch video on the internet to make sure i was building it the right way, because the manual was not 100% for me, i had "?" a few times
This is my first printer and i knew nothing about 3D printing, building it is the first step, then you need to calibrate it,
you have to learn the software and all those printing settings.
there is a lot of tweeking and learning for the newbees like me.but you have to solve those problem one at the time
after i found out how important the distance between the nozzle and the bed are, and alevel bed is also very important.
i think most failed, result of a bad distance between nozzle and bed and bed leveling
at 500$ it is cheap and lot a people have the cash, but you need a basic kit of skills to be successful with this
if you don't have them, just get up and learn!
A 3Dprinter is a precision machine, you can't cheat
stuff that i replace , stepper driver 5 for 10$, idlers pulley 5 for 10$.
in conclusion, that kit has flaws it's not perfect , but nothing to prevent you from 3d printing, be prepare to upgrade some stuff on it.