My first kit for about 15 years and apart from discovering I'm as blind as a bat I've discovered that Airfix have not improved over the years, what a piss poor quality kit, it's more like a toy and the flash, mould and distortion is amazing.
I reckon you could still turn a decent P51 out of the Airfix kit. The u/c needs beefing up though - can't really stand the weight of the completed kit. I've had mine (made for me by my Dad) since it's first release in '74.