Hi Euggy,
ZING:
The price you mentioned is unrealistic. There is something wrong. A machine like this in a working condition should sell for around 6-7K. It is a very reliable, high-quality machine with excellent support. The engraving quality over wood veneer would also be excellent. If 2mm is your max thickness a true 30W should be fine. Keep in mind that the tech. spec. of K40 are intentionally false. The tube of K40 is actually below 30W. Unlike the cheap Chinese machines the Epilog laser tubes can be refilled (repaired) if the laser start loosing power after several years of active use.
As an alternative to ZING you may check RAYJET. The quality, prices and support would be very similar.
LG500:
Personally I wouldn’t trust this machine for precise, quality work. It is made to be cheap by the Chinese standards for cheap. That would reflect on everything - the quality of the components, the quality of the assembly, reliability, support, etc. If your business would depend on the performance of your laser machine, I would suggest to look for other options.