The cheap chinese machine electronics are a lottery really. Some work fine some fry in days or weeks.??
Common problems are cheap brittle wires cramped into too tight space and poor grounding. With a little re-wire these are sorted quick enough.
elelcronics side ie: Drives PSU then like I say it's a lottery and if they die then just replace with newer decent gear.! . . simplizzz.

The Type of connection and Pc spec however matters to how well the machine works. The PP is slow and unreliable. It does however easily keep up with these low spec machines. Still however I wouldn't use it if could afford the better option.
I also wouldn't go with USB if taking the better route and would go with Ethernet for all the connection and stabilty options it gives.

Now your Other problem which you may or may not be aware of is that Mach3 parallel port driver doesn't support 64bit OS so if your thinking of using it then you can't and you'll need XP or Win7 32bit. Both work fine.
Mach3 the program will work fine with 64bit OS but the Parallel port driver doesn't. External motion control cards however like the ESS etc don't use this driver and have there own Plug-in to control the device and happily work with 64bit OS.