I’m guessing “Grip 6” is a particular brand, but I have used buckles with grip action (on normal leather (or were they some fake leather? dunno but not nylon) belts without holes) quite a bit and I liked them.

Making your own holes in a holed belt might cause a greater structural weakness than it can handle, depending upon how tight you like it.

I recently got a knitted-ish belt (this is probably nylon or similar stuff) and you can insert the anchor at ~5mm intervals (thickness of the rope used to knit it) and that seems like a good idea too.