I'm guessing the main intended use-case would be for what they mention in the review, that is for"laptop users who don’t want to haul an entire mechanical keyboard around with them."
I could see that actually making some sense, as the positioning of a laptop's built-in keyboard can be less than ideal for gaming, as you can't reposition it to the left of the screen, and the keys may not have ideal gaming characteristics either. And a larger keyboard would need to be placed either over or in front of the laptop, neither of which would likely work all that well with most setups. With a half keyboard like this, you could keep it directly to the side of the one that's built-in, and that keyboard's keys would still be accessible for anything requiring them.
For many games though, this could still be problematic, as you would have to reach a lot further to access those other keys, and there may not be enough keys available to remap everything how you would want for some games with more complex control schemes.