I've been using one on my Orbea Gain since 2018 and I'm still here!
There are three things I don't like:-
1/ You DO take your eyes off the road to look down when you change power levels
2/ Forward planning is everything, as in looking ahead and not taking your hands off the bars when you're approaching a rough section of road or your going downhill very fast and realise you've got an equally steep uphill coming up and want to be in a higher power band. Again taking your hand of the bars probably isn't the best if ideas.
3/ You have to cycle through the power level to go to a lower power level.
In practice you get used to it.