OK I sent myself through as a guinea pig (also I couldnt find a printer).

Security/TSA check point was fine. It scanned the boarding pass on my phone like it would for any other airline.

However when I got to the gate, Frontier staff didn't seem too familiar with e-boarding passes (maybe noone uses them).

My phone wouldn't scan, so they typed in my seat number to the computer.

So it looks like it pretty much works. If I find a printer before I fly back, I may just print the boarding pass to be on the safe side