Don't get me wrong, I love Chinese lasers (I have more than enough of them) but there are some jobs they are simply not suited to, particularly the lower powered small format machines being used to cut thick materials. On a DC machine I rarely if ever cut anything thicker than 1/4 inch no mater what power tube the machine is fitted with (2 of mine are beam combined tubes with 300 watts+available).
If I want a nice smooth edge I'll use one of the RF based machines, if I'm just ripping out basic 3mm MDF or ply etc it gets shoved into one of the Chinese boxes with their DC tubes. Like Kev I'm happy with what the Chinese boxes will do for me, they pay for themselves on pretty much a monthly basis but I'm also not under any illusions that they are something they aren't or that they will produce the same standard of work as a Western/German or Japanese machine will.
Maintaining them....I basically don't, I run the guts out of them, keep the optics clean then buy a new one when they break as by then they have paid for themselves many times over.