I think you've already nailed the analysis. Cheap chinese boards often have issues with substitution. FET's might not be beefy enough to drive a heated bed, chip might not have the bootloader burned on it. It will be a bit of a crap shoot whether the board you get will work first time or not. If you have good electronics troubleshooting skills and are familiar with burning the arduino bootloader and loading firmware you might find that the cost savings is worth it. If you want something that is tested, and supported, a local seller is more likely to be what you need.
Bryan
Bryan