Vow of Poverty, overpowered or underpowered?


I have read plenty of things about the Vow of Poverty in forums, and i have seen both opinions expressed.

If i understand it correctly, it does work on the assumption of a linear magic item acquisition from the rest of the party, and it is "balanced" on that assumption. I also do understand that some builds use it to mix/max their character, with synergy of other vows.

My question is, as a mechanic, and if one assumes that this linear magic item acquisition is valid for a party, is it overpowered, underpowered, or balanced. Are there any other aspects i am not aware of?