You are not the only one disappointed here.
I too was a SiteAdvisor user, namely Firefox plugin user, until yesterday when I allowed it to update, after which I found out it had installed more than I had asked for w/o asking for permission. (Later I found out it had broken IE7 apparently.)
It seems the days of standalone Firefox plugin are over, as the current installer available installs this new monster (IE/Firefox plugins + System service), user has no choice any more.
You should give WOT a try

happy Devs are responsive there and their plugin is just plugin. Staff there participates actively in the forums, which is a nice bonus.