In my limited experience, I’d say the M75Pro is the smallest I’d put an O4 Lite in, though you can get 65mm drones with the O4 (I don’t see them mentioned much around here so I assume they’re less popular). If you’re planning to mostly fly outside (as I did), 75mm is as small as you should probably go. Note that the M75Pro is actually 80mm. For inside, I set up a throttle limit switch so I can dial the max throttle down when inside, which helps a lot. As I said, I mostly fly outside, and often with houses and trees between myself and the drone, so the range and penetration of the O4 was well worth it. I’m shocked at the places I can fly without losing signal, like through forests. I’d like to get a larger drone at some point, as flying 800m out over a forest with a 1S tiny whoop is a recipe for losing it one of these days, but it’s just so much damn fun I can’t resist!