Cool, but not worth 12 Euros. I'm sure it's worth the time and effort they put into it, but there's really no use for it. If you really have an urge to print something on a Game Boy Printer you're better off creating it on the Game Boy Camera and then printing it from there. Odds are if you have a Game Boy Printer you already have a Game Boy Camera, anyway.
Great video showing how to cheap and recycle old till rolls. What next? A cable to attach the spark printer of the Sinclair Spectrum?