I had a Moto 3i and I felt it needed one lower and one higher since the choices are 3 and 7 I went with 7. I really like the 34 tooth low and the 14 high was fine. I swapped it out for a 34-11 as I liked the wider spread. I always hear about the "Complexity" of a rear derailleur but have never had issues, its a cable and 2 limit screws done. I cant see having 21 or 14 gears on a cruiser but its nice having a few for the hills and better to have a few extra you dont use often than always running out....and the 7s are less expensive.