Should I have reservations about using cashapp to collect rent? I have 4 units now that are spread out an hour apart. I know I could get a post office box, but it seems so much quicker and easier to collect digitally.

I personally use cozy.co. Its free for both landlord and tenant(as long as they use checking account to pay). 

I also recommend Cozy. 

Cozy allows tenants to pay by credit card, for a fee, if they are short cash. It also allows you to charge late fees. 

Cash app does not offer these options.