If you mean Miyoo A30 is hard to hold or something so that's why it's "inconvenient" then I can say GBA SP shaped ones are better at grip for long time and gotta say adjustable tilt of their screen matters a lot (I played GBA SP a lot on public transportation so I know).
- Anbernic RG34XXSP's screen is 3:2 like GBA, so because of any console that's games are not designed for 3:2 which is non-GBA games will have vertical black bars or weird stretching on screen so it would suck that non-GBA game screen getting smaller due to aspect ratio. If you wanna only play GBA its hardware is weaker but has 1 more GB RAM so from price point it may be cheaper alternative, however demanding console's emulators may run stably when emulator asks for more RAM (more RAM is always better for emulation).
- Miyoo Flip's screen is 4:3 which is pretty much standard for most of old console gaming but it may have horizontal black bars for GBA games that will make its screen smaller (or even a tiny screen in the middle of black bars everywhere at edge) or it will stretch the screen to make 3:2 look like 4:3, if it bothers you then better don't pick this one. Has 1 GB less RAM but in general its hardware is powerful, however due to having 1 GB less RAM demanding emulators may don't run stably.
So if I had only wanted to play GBA games and somehow I can't buy GBA SP, NDS or 3DS and can't use mods to play me ROMs then I would buy Anbernic RG34XXSP.