They were the only cheap and quite accurate way to play your original carts. Since they've stopped production the only alternative now is Analogue Pocket I think, and that cost is sky-high

Back in those times, when the screen mods were just biverts, you'd either do that for a modern lit screen, or pick up a GB Boy. Funny name, but they were actually very clever and the only real (almost) 1-1 copy of Nintendo's own systems

Quick edit

These were fairly universally mocked when they were sold, just because of the name, but now they're gone everyone is sad they didn't pick one up!

That was not the only issue. It has some little sound issues in some games (Tetris IIRC) and the aspect ratio of the screen is wrong.