Can won't give you any measurable hp gain. Only weight (and perhaps hearing) loss. Lots of guys like the thing. MBRP makes a popular one as well. SLP makes all kind of Polaris stuff that seems to work pretty well.
If you want something loud go with an MBRP I had one on my 06 700 and that thing would make my ears ring. It was to loud for me so I took it off and put on an SLP.