I picked up a Funduino Mega a couple of months ago - it's a clone of the Arduino Mega 2560. I have it running my Prusa i3. However, I have had one problem - it really wasn't properly operating unless plugged into USB - there was some kind of problem with the power. This manifested when trying to print stand-alone from the control panel and SD card - the panel worked but was very faint, and the motor drivers didn't work at all. If I plugged into USB, even just the hub with no computer, it worked fine.
I finally sat down and figured it out this evening. The problem was that the 5V regulator that they used on the board was mislabeled - it was a 3.3 volt regulator. So both 5v and 3.3v lines had 3.3 volts or thereabouts on them.
I hacked in a 7805 (see photo below), unfortunately lifting a pad in the process so I had to put in a bodge wire to take care of it. It is hard on the board since it's designed for a smallish regulator and the 7805 is large and the pinout is wrong, which is why it's mounted in a weird way.
Anyway, the board is working fine now. I should probably blob in some silicone snot to hold the thing in place so it doesn't vibrate the traces too much.
There are a lot of < $20 Mega compatible boards on eBay right now. I doubt any of them have any better QC than the Funduino, so be sure to check this when you get your board, it can seem OK at first especially if you are using USB so the board gets its 5v from there.