Ah, yeah, I remember now. Sounds interesting. That armor restriction will most likely hurt a lot in BG1 and be almost irrelevant in ToB, I think, so you may want to front-load the Spin progression a little to counteract that.
It's powerful, true; especially on someone who already has a high Strength (the jump from 15 to 17 isn't nearly as significant as from 17 to 19). But I don't think it's in any way OP, considering that you can get two one-handed +2 weapons with an extra point of elemental damage as loot just as early in the game, as well as buy +1 shields. That extra AC matters a lot, especially when ogres can one-shot you.
Although, my Inquisitor managed to chunk Mulahey in two hits with that thing. Mainly because she landed a crit for almost 50 damage, so it was mostly due to Mulahey not wearing a helmet. (Seriously, man, you're living in a mine. What were you thinking?)