This Gameboy version of Bonk is a mix of elements of the first two PC-Engine games, with mostly all-new bosses and different levels (that still resemble similar levels in the earlier games). It doesn’t feel like an entirely new game, there’s too much reused content, but it’s also quite clearly not a port.
That said, playing Bonk in black and white does have its own charm. The lack of colors emphasizes the graphics and the controls do seem to work even better than on the PC-Engine. Of all the Bonk games, this is probably also the easiest, since the bosses don’t pose much of a challenge. Still, it’s fun to play and that’s what matters.