Square Cash is currently #38 on the chart for top free apps in Apple's app store. No other financial apps above it. Might be good momentum with that product at least.
https://www.zellepay.com/partners
While I think Square has some momentum, I believe the financial services industry as a whole is going to overshadow their Cash offering.
I've literally never heard of Venmo before now
I know for me personally I'm far more likely to say "you get it next time" than bill my friends for some share of an outing. If it's sufficiently expensive that this doesn't make sense I'd just split the check. If I was younger and still a student I can absolutely see the appeal though.