Really REALLY not liking this idea. Why should we have to PAY you to HELP you? I know of no other game that does this. You limit the number of people that can test things, you divide your playerbase and not to mention, you just plain old screw your customers.
Seriously, this isn't like early access. Game is out. This is seriously, deeply concerning and makes me question supporting you and any future endeavors in the future.
No one is twisting your arm. They have plenty of testers already. Would you prefer it if they slammed the door down?
The nature of a Beta test is that you can't have all 300,000 or whatever players testing. It has to be done with a smaller sample of players. How would you prefer it chosen? At random? Only the coolest people?
It's a simple way to ensure that those testing are serious about testing, and makes perfect sense. There is nothing wrong with it.