I bought the AV turret with certs as soon as I could possibly afford it, and it's awesome
I use the fire into the air method to get a good trajectory... and yes, you can hit things around corners, and over walls, and around the stanchions of the spawn building rooftops, it's amazing if you get it in the right spot
That said, there's no shield, and I'm actually squishier in the turret than out of it due to no mobility and my flak V not being taken into consideration... also, you can't really surprise good tank drivers with it at close or even medium range, one shot is all you'll generally get before you have to reposition.
The range is amazing, if you can see it, you can shoot at it - doesn't always mean you can hit it as the turret has no zoom so the further away a target is, the more you have to account for not being able to land the rocket precisely on it, and that's where the fun part comes in, you can make them swoop along roads to zap a tank in the rear that's trying to get away, you can make them hit anywhere you like, essentially, you just need time and practice and not to get headshotted whilst guiding the rocket (although if you're on your target and get out of the turret or get killed, the rocket continues to that point so you'll get the hit/kill if the target doesn't move)
From what I've seen so far, good AV turret users will be a little like good snipers, only a lot more detectable