I agree that cash is, and will always be, king. Especially in this industry.
However.....money transfer apps have a convenience factor for me in that it's that much less cash I have to go and deposit into my bank account.
Cuz...ya know....bills get paid online. Gotta have moolah in the bank to do that. LOL
I also have clients that find it most convenient for them so that they don't have to take the extra time to hit an ATM on there way here on their already limited time budget.
Then there's the guys that use the vanilla visa GC's that they are gifted by their clients as payment for sessions....
Meh....payment is payment. Whatever is most convenient for my clients, I'm cool with.