Yeah, I tried it on a 1.99EUR SXF-PMI fare booked specifically to test the app.

Was quite funny to watch on the seat reservation screen in the app how Ryanair was slowly filling middle seats first

I checked in 2:50h before departure and got an aisle seat in the front. And after check in, the app even offered me to buy a different seat if I didn't like the one assigned - this means if you don't win the "lottery", you can stil buy a decent seat, albeit at a higher price (the app wanted 10EUR from me).