They include sites that seem to be their competitors because they earn referral fees when you buy memberships. A couple mentioned in scam forums even try to dupe you into buying the same list at other membership sites they own under different names. Naturally, these sites also have an incentive to exaggerate how much you'll earn from online paid surveys.
With one of the lowest cash limits in the industry, you can get $10 out when you have accrued just 100 points. If you want to take your earnings in the form of a giftcard, the threshold is even lower, as you just need 50 points, equivalent to $5. Many other survey sites will only pay out after you earn much more, like $50. As with all good survey sites, Opinion Outpost allows you to take your earnings away in vouchers for big firms like Amazon or iTunes, or if you prefer money, to do so through Paypal. As well as paying out early Opinion Outpost also pays extremely quickly, often the same day or in some cases, immediately.