I love both bands and saw them both in concert. Tool albums "Opiate," "Undertow" and "Aenima" are awesome and Perfect Circle's first album "Mer De Nom" is a classic......unbelievable sound and very aggressive...just like "Undertow." While Perfect Circle is great, they only have two albums and the second one "13th step" or whatever, ain't that good. It's just that Tool has much more material. Give Perfect Circle a few more albums and I bet the comparison will be much closer. For those people who don't have the albums, get "Undertow," "Aenima" and "Mer De Nom." You won't regret it.