Public beta-tests work.
There's never a shortage of volunteers at least for the ones I've been involved with. It's kind of cool as well when you report a bug and it gets fixed it makes it feel like you have something invested in the product and somebody cares about your input. The more worthwhile your input it seems the earlier you get the test versions too. Companies that adopt a policy of public betas obviously take note of who is contributing positively.
I'm always bound to an NDA and stick by it, but when the product hits the shelves there's no secrets anyway. It just stops some of the frustrations that early adopters end up having to confront. I've not come across a downside.
I don't mind the good people here paying to do it though, I can always jump in if/when I feel the quality is high enough at the appropiate *FREE* bugfix update time.
As for totally open public betas is there even such a thing? All of them require you to apply and you get called in somewhere down the line, at what point is often dependant on whether you've contributed to one before, that's true of all companies that provide them. So certainly Studio One and Bitwig do public betas in any known sense of the idea. Also, whatever product category somebody wants to put Reason in, the bottom line it is one of the most robust software products out of the box at release time there is. That is the whole point.