As a retired machinist, I have something to say. I see people saying things about accuracy and flatness when talking about these small machines. I think, not knowing for sure but from experience that a lot of it is caused by the owner/operator of the machine.

Some of that is certainly true.. some if it is in the tolerances/quality of the machine too.. Those spindles typically have quite a bit of runout, there is slack/backlash in the bearings/lead screws,etc.. they aren't being trued up on surface plates.. aluminum extrusions certainly aren't perfect/true,etc..
dial indicators certainly aren't in many users tool bag nor the knowledge to use one properly..
These machines are put together from a box of parts.. Most aren't referencing/fixing everything off a solid datum,etc..
Then there is missed steps,etc... from overdriving the motors due to speeds/feeds not being correct,etc...
Tool deflection,etc...

Its sure easier to blame the Chinese machine though than to admit one isn't experienced or aware,etc...

 

Yet I started with no CNC experience at all and with a £321 machine I produce pretty good PCBs. I use rivets for 'plated through' holes which are quick and easy to use and thin enough to put under components. I use a green spray coat to protect and 'beautify' the boards: http://www.fortex.co.uk/product/green-coat-solder-laquer.

 

Some of that is certainly true.. some if it is in the tolerances/quality of the machine too.

And don't forget many of them don't come with any kind of owner/operator manual.

Years ago I bought a high dollar power miter saw from a guy, because it didn't cut square or true 45 degree miters and he got rid of it real cheap. He never dialed the thing in. After setting all of the adjustments correct there was nothing at all wrong with it. And the manual for that saw even told step by step how to do it. But he figured it came from the factory ready to cut.