Just been looking at these type of addons (used to use SiteAdvisor back in the day and liked it originally) and most seem to suffer from the same issues of user/bot review spamming and manipulation, large numbers of false positives etc. Are there any that actually are worth using or are they all just a waste of time? (I'm suspecting the latter but someone may surprise me )
Along with WOT I've liked AVG LinkScanner (freeware) which can be used without their whole super-sized anti-virus suite, I however use WOT because it doesn't show any adverts.
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Edit:
Forgot the question of are they all inherently flawed. What I've seen using SiteAdvisor, AVG LinkScanner, and WOT is they may flag some sites the same and some not. I like WOT because it has different levels of safety; Trustworthiness | Vendor reliability | Privacy | Child safety
I combo Site advisior with WOT, but the former stopped working with firefox 5.1 soooooooooo