I don't expect a standalone GBA. Rather, I was explaining what I would buy.
Since that's exactly what my GameCube is these days, I don't need such a thing and it would never replace the real hardware. But such a thing would get my curiosity going which is the only reason I have any interest in this thing (A feeling I suspect you can well understand judging by threads like this and your YouTube channel).
It wasn't confusing, just was seeking confirmation that it was indeed emulation like I thought and that you weren't able to somehow interface this thing directly to a Game Boy or Game Boy Color rom image via your GBA flash cartridge or for some bizarre reason were able to make it interact with a GB/GBC flash cartridge (If one existed?) where it did nothing with the actual standalone retail cartridges.
Do you happen to have Activision Anthology around? I'd be curious to see how that one panned out or any of the NES Classic/Famicom Mini lineup or similar commercial emulation releases like the Capcom collection. Partly to see how well they translate and partly to see what you think about how they look when this expands them back to their original 4:3 proportions on a CRT.
Not only are they a good stress test of this (As is any emulator), but I imagine the missing horizontal lines of resolution on the NES releases (Done of course to adapt a 4:3 game to a 3:2 AR) will provide a rather strange appearance on the big screen and running in full 4:3.