Venmo is quite easy to use IMO and I didn't feel it is particularly insecure because it is backed by PayPal. That being said, a lot of my friends just use Chase QuickPay to transfer money, which works really well. TBH, I don't know how a potentially device/OS restricted service is going to play here. Maybe they need better PR to <i>educate</i> Android users to install their app.
Experience-wise, I have used both Venmo and QuickPay (and Apple Pay). I would much much rather use a P2P version of Apple Pay than either of the other two. Agreed that it would be yet-another service I'd have to use, but I already have to switch between Venmo and Chase Quickpay and others.
In addition, there are well-known cases of Venmo being insecure by design, because it relies on interbank transfers. The response from Venmo is that you should not use Venmo with people you don't trust, because the money can be clawed back. So, for example, for receiving payment for an item you sold on Craigslist. I highly doubt Apple would put its name/the TouchID brand on a service with similar pitfalls.
Paypal has a history of tying up their customers' funds for no good reason. They've done this to online fundraisers in the past, and even attempted to coerce a campaign benefitting the Red Cross into redirecting donations to the United Way in 2005. I refuse to do business with Paypal or Paypal-related companies whenever possible.
