I rasied this awhile ago about AFPx. I don't think it was ever intended as a tool for the small VFR or evn IFR flyer to put online plans in but rather as a tool for airfields and FBO's with staff and a fixed installation. It is the tecnhogeeks amongst us that have seized on it as a way of filing plans when operating from our private strips and unmanned aerodromes.
I have used it quite a few times for IFR planning and it works well enough if you are prepared to carry the laptop and sign in.
But at the end of the day I have gone back to the good old method of sending a plab to London and letting the team there deal with it. Always works a treat.