They are GREAT! My 40 sized P-51 is done perfectly with the exception of the fuel tank. My fuel tank slip right along the seam and soaked the front end of the plane with fuel. I got most of it out so it's not a problem anymore. I would get a Hayes slimline fuel tank to fit your Extra just to be safe. Then just glue a thin plywood plate over the hole where the front of the fuel tank pokes through the firewall, and then drill 2 holes in it for the fuel lines to go through. With that done, the airplane should be nearly perfect. The hardware that came with my P-51 was very high quality, and works great. The airplane is also very easy to fly for a Mustang, and is plenty strong for the OS 70 up front. Extras are a little "different" too so I think it should be just as good. I've seen the World Model PT-26 and it was just as good with the exception it had retracts. The real PT-26 didn't have retracts, at least not the ones I've seen at airshow. The PT-26 and my Mustang will land slower than scale. I can't get my Mustang to tipstall either. It will gently drop the lower wing in a slow, steep turn with some up elevator, but at those speeds you are too slow for scale anyway.

Bottom line, you'll love it!