Nope, no fees at all for the Alpha/Beta prepaid service.
Yes, this does mean they’re almost certainly losing money right now (thanks investors, I genuinely hope you make your return or whatever you’re looking to get out of it long term!). The difference between Monzo and other prepaid cards is that Monzo is only using the prepaid product as a stepping stone to launching as a full bank with current accounts while other prepaid cards are sticking with it. As for how Monzo plan to make money as a full bank, check out this thread.