I've brought my Stratus on several trips. Inside an airliner, you'll really only get signal if you leave the thing pressed against a window the entire trip. Otherwise, you probably won't even get GPS lock, forget about ADS-B. TBH, there really isn't a lot to see once you get further away from the airport.
No one has ever made a fuss about me using it, typically they are just more curious as they see whats on my iPad. Once I was sitting next to an off duty captain, once he saw what I was looking at we ended up chatting the entire trip.
So... generally it shouldn't be a problem, but you should always follow the direction and instruction of the flight crew, commercial or not.