Just done reviewing the new GBA EZ Flash Omega. It features quite a few cool extras not normally seen on a flash cartridge.
My GBA is a JP AGB-001 modded with an AUS AGS-001 screen, and the EZ Flash Omega has some kind of issue which often (but not always) breaks game saving. The devs say that it's due to the mod ("electric leak jamming"), so anyone with a similar setup should beware. I think AGBs modified with AGS-101 are confirmed to work though. Works fantastically on my NDS though, so that's how I use the EZF Omega.
About the GameBoy/GBC support - is that via emulation on an NDS or is it somehow running those games natively? edit - no matter, just watched the video in full, and it says it's emulated. - In which case, how accurate is the emulation? Also, do the saves work the same way the Omega handles GBA saves?