I haven't upgraded anything yet, But I am about to stick a couple of Blade grips on the milling machine to open them up so that Blade CP rotors will fit. I need some blades that don't have a fragile monokote covering to tear up everytime it hits a blade of grass, and can't justify $70 carbon fibre units for the Axe. There are some plastic blades for the CP that cost about $24.
I'm also looking forward to installing a heading hold Gyro. I'll put the O-Scope on the Axe and CPP to see if they can use the same gyros.