It's not a "good deal" in any case....
The minimum purchase price on iOS is $0.99, so at worst you'd be paying basically the same rate (~30%).
But most payment processors offer separate pricing for micro-transactions (e.g. Paypal is 5% + $0.05 IIRC). Which works out at around 10% for a $0.99 transaction.
And actually - Adyen offer much better pricing than the "Stripe rate" of $0.30 + 2.9% in the first place.