This one is a weirdo.
It worked on 2 out of my 3 custom themes (the submit button wasn't there when it didn't work). I noticed many people complained about that.
Anyway, this is a VERY powerful contact form so if it works there is more or less no need to look elsewhere.
4 stars because it may NOT work + you can only send emails to the official admin email in the profile, you can't just put in any email address (wtf?).
All in all a damn good plugin.