Horrendous. persevered for 3 days. Felt unatrual. Very hard to grip the rest of the controller with the extra height of the thumbs. It ruined my original rubber which was in perfect condition, biting chunks out of it with its grip.
It does what yuud imagine though, makes moving the sticks a lot less effort. Leverage is all it is. If only the original ps4 thumbs were lower in the first place then the additional hight wouldn't be an issue. And it'd be a good concept.