so ive been going back and forth on this for a couple weeks now. i have a 2019 honda fit and im trying to get a decent 70cm setup going for some local linked repeater stuff, maybe some satellite passes if i ever get my act together on that. the roof is an option but honestly drilling a hole in a car i still owe money on feels real bad. the lip mount seems like the obvious no-drill answer but ive heard mixed things about ground plane with those and whether it actually matters on uhf.

the antenna im looking at is a diamond x50a which i know is a collinear and not really optimized for 70cm satellite stuff but for now im just doing terrestrial repeaters so gain pattern doesnt bother me much. just want to know if people have actually had reception/audio quality issues with a lip mount setup at uhf vs a proper nmо on the roof. the car has a pretty flat roof so mounting position shouldnt be too bad if i go that route

ran a lip mount on my old civic for about two years on 440 and honestly it was fine for what youre describing. local repeaters, no real complaints. the ground plane situation isnt ideal but at uhf the wavelength is short enough that a little compromised ground plane doesnt tank your signal the way it might on 2m or lower. i switched to NMO eventually mostly because i got a new car and just decided to commit, not because the lip mount was giving me problems.

one thing i will say — pay attention to how tight the lip mount clamps. some of the cheap ones vibrate loose and you get that horrible scratchy noise while driving. i had that happen once and spent an embarrassing amount of time thinking my radio was dying before i figured it out. the comet ones seem to hold better in my experience

x50a is a solid choice but just so you know that thing is like 3.5 feet tall, parking garages are gonna be an adventure. just something to think about with a hatchback since youre already lower to the ground than a truck or suv would be