From my experience, this really depends on their target focus of the feedback.
The feedback from the exchange beta gives a pretty in-depth idea of how people use the trading aspect which is where complexities lie. These are best suited for lots of people to test.
When it comes to mobile development you are often stripping everything down to the simplest forms in the most intuitive way possible. Surveys give you the best idea on “how” people intend to use the UI but a closed internal beta with a small pool is often the most effective because studies have shown with just a handful of users you can find out over 75% of the general feedback right away that you would get from testing with thousands of users. Since the feedback they would most likely be looking for is things outside of trading itself (i.e. Nash Pay, etc.) this is most likely served best working with a small number of testers with very precise feedback.
You don’t really need 1000+ testers to arrive at something like apple pay just really good UI/UX designers who understand their audience and a few testers.