Does the GBbook work on a real Game Boy?

Yes. That is the intended core use case, not a secondary possibility. GBbooks are conceived as real cartridges for actual Game Boy hardware, which is exactly what gives the concept its meaning. The point is not merely to simulate a retro reading experience in theory, but to make the cartridge function as a physical object connected to the original ecosystem. Of course, anyone with a very specific hardware setup, modification, accessory chain, or non-standard use case should still ask before buying if compatibility is especially important. But in general terms, the whole project is built around real console use, not abstract digital consumption.

It should be compatible with the original Game Boy Color, Game Boy Advance, Game Boy Advance SP, Game Boy Player, and recent third-party consoles that can read these cartridges, such as the Analogue Pocket. Not compatible with Nintendo Game Boy DMG (original 1989), DS, DSi, 3DS, or later Nintendo systems.