Ah - I kept wondering what the main hook for these services was, appreciate efficiency and social effects are the USP, but wondered what the main reason was over and above just a direct transfer from your mobile banking app (how most people I know here in the UK do this).
* If I know their bank routing number and account number, I can just send them money directly without any involvement on their end.
* Most people will not just give out their account info, even though it's on every check they write.
None of this would be a problem except that each bank uses a different system. Chase uses ChasePay. Ally and PNC use PopMoney. There are several others. This causes a lot of friction when sending money. "Oh, you use chase pay? Now I have to set up an account there, too."
Venmo (and others) let you abstract away the bank details. Everyone in your friend group signs up for 1 account (and it could be a competing service. I like Sqaure Cash) and is ready to send. They also offer better account lookup and the ability to send a payment request.
They also often require using a clunky web UI without an ability to do it from a mobile app.
I prefer square cash, but this entire app ecosystem only exists because American banks don't allow free wires for some reason.
The only people I know who use google wallet are google employees.
As far as trust there's pretty limited risk, lots of protection/laws around bank access and easy to audit.