I finally got my GCW Zero a couple days ago now, and I'm loving ReGBA even in its early state.
It runs very well, I have noticed the occasional issue like misdrawn text in Mario & Luigi Superstar Saga, where text drawn at 2x scale might be missing a horizontal line.
Sound has improved with alpha 2, and I'm enjoying the 1:1 display option. I hope that you can include an aspect ratio upscaler though, something that doesn't skew the aspect ratio. The fast forward option is a great demonstration of how effective the GCW Zero is at emulating the GBA.
I hope you can include a way to remap the controls sometime, since the A button on my system is somewhat stiff, when pressing down B as well.
Can I also suggest an alternative keybind for exiting the application? Something that's quite unlikely to be done accidentally, like analogue nub left + X + Y.