A while ago I bought one of the cheap Chinese cutters.
The motion controller was a piece of utter junk -parallel port, and flaky as hell - had a habit of freezing part way though a job with the beam on, setting the work on fire. It had no speed control, which you need if you want to do more than simple surface engraving. Also had no height adjust.
The mechanics were sort-of OK, but the optics had no fine-thread adjust screws so alignment is a nightmare to do.
The cooling they provide is a pump you put in a bucket of water - you really need to hook up something more permanent, and enclosed so it doesn't fill up with dirt and gunk. You also need to add some flow detection, otherwise if it gets blocked or leaks you may not know til the tube dies.
The extractor fan they supply is pretty crappy. You _need_ extraction.
Although good for acrylic, that, and thin card & ply, is pretty much all it's good for material-wise.
I subsequently bought one of the cheap 3040 CNC engravers which has proved much, much more useful - much wider range of materials, depth cutting, ability to use for precision drilling of PCBs, jigs and cases, PCB outlines, and potentially also solder paste dispensing.