The underfolder works, but I'd agree with BSW that it's not the most enjoyable and ergonomic solution to a folding stock design.
As for the Yugo rifles in general, they're somewhat different than other AKs. Heavier weight/thicker receiver, which some people like. Non-chromed barrel (even back when you could import original barrels), so you need to be a bit more careful about cleaning if you're shooting corrosive ammo. The front end furniture is a bit different than other AKs, so if you're inclined to replace it with something else you have to make sure it specifically fits an M70.