One thing to note about all BA Cityflyer flights is that overhead storage space is pitiful for standard cabin bags. They only fit sideways on so it is nigh on impossible to accommodate bags from all passengers. So long as you are not in an emergency exit row you can stow under the seat in front of you but this obviously compromises legroom.

The best way to avoid this is to ensure that you find your way to the front of the queue for boarding and then hurry to board, unless you are prepared to check luggage.

I flew AS on a Q400 a couple of days ago and really liked their "a la Cart" bag service where you surrender your cabin bag at the aircraft steps and receive it back in a similar location when disembarking. BA Cityflyer could learn a lot from this approach.