Trying to make a long story short, I bought a P4 from Best Buy and it had some sensor calibration issues and a GPS warning when in forward flight even after a successful calibration, so it was returned for unit 2. This one flies ok, but one of the motors feels a little stiff compared to the others. Doesn't get hot, just doesn't sound or spin like the others. It isn't notchy or gritty, just doesn't feel right. I'm contemplating taking it back for a 3rd one, but is that being unreasonable? I've had one before and all the motors were silky smooth. What's an acceptable margin here in what to reasonably expect? The motor could potentially fail in the future sure, but who's to say? I really don't want to take it back and get something potentially worse and then what?