never dont CPA at all, but found it eye opening when out with some other affiliates on a trip, with one person from probably the biggest sports affiliates in UK, and they had most of the bookies on CPA back then. remember him say we might go on rev share if the bookie can prove they can manage...
some slight positive gains on 1 site, but nothing on another, but it's still early doors. i had a nice boost with the last update but then it slowly dropped back after a few weeks
well that depends the quality of that traffic. you could send thousands of registrations to someone but make next to nothing if your traffic is garbage.
I'd say someone who dominates the SERPS but also has a specific product that people go to, and want to use no matter what position they are in. think something like oddschecker