So FTers who actually fly on one can comment on their experiences here.
I actually flew on one. It was on WN though, I think MDW-TPA, during the week or so between when the EU and the rest of the world grounded them, and when the FAA finally did. I didn't realize I was on one until I got to my seat and saw the safety card labelled 737 MAX (all WN planes are similar in a 737 kinda way).
I would be fine with flying on one now after the re-cert process, but TBH I was a bit apprehensive that day until after several minutes into the flight (since it seemed like the MAX crashes happened pretty soon after takeoff). Flight was uneventful. I think the FAA finally grounded them the next day.