We've been off cable for about a year and I went through last season streaming the games I couldn't get OTA. It worked ok for the most part, but at times it would buffer and I had trouble connecting to the servers, as in it would just hang.
I thought about getting cable just for the months football is on and cancelling when the season is over. If you don't sign up for any promotions it's pretty easy to do.
I wasnt using Sling or Roku, just connecting directly to espn. We had two houses at the time in the transition up here so I just used my EPBFI we had in Chatty to sign in up here.