Thanks for the quick reply! I've done some testing, and at least OnionOS for the Miyoo only recognizes the .gb file, so I'll use that one.
I also started to play Batty Zabella and I like it very much! Especially the humor, which IMO is one of the most difficult parts in a game to get right.
Actually, it's also my first Gameboy Game ever, because I never owned a GB and thus, also never emulated one. But I think they're perfect for the modern emulation handhelds, and thus, when I stumbled upon your very appealing GB game, I took the opportunity. And I haven't been disappointed. Thanks for supporting the GB world up until today!:D