Up to 4 unbalancing criticals per round and still get a 60% attack?
Hardly. As written in the book, a character can melee scuffle before or after his normal attack. It implies he may only make
one melee scuffle action if he performs a normal attack. This reasoning is enforced by the fact the text mentions he may perform
two melee scuffle actions
if used with weapon brawling and up to
four melee scuffle actions
if he performs no other actions.
Anyway, I use the skill, with pretty much all fighting class characters having developed it and it's hardly OP. First, because it's a still a skill one has to develop. Second because with "pretty much all fighting class characters having developed it", it balances itself. That being said, I have to admit I put two restrictions:
1) One may only perform a melee scuffle action on an opponent of the same size category (no, a human being cannot hope "push around, trip and throw" a dragon!), with non-bipedal giving a penalty to boot (because a quadruped is harder to "push around, trip and throw" and the skill was obviously thought for humanoids fighting each others),
2) Success is determined by comparing the melee scuffle roll (because if only the ranks are used, why even roll the skill?) of the attacker to a "pure" weapon roll ("pure" as in "no weapon bonus") for the defender so that highly skilled (in their own weapon) characters are harder to affect through a "melee scuffle" action.