Steven,
I have read and heard (podcasts) a lot about Jerry French, Ed Ward and the rest of the Testosterone Gang that came up with the Intruder and Jerry still prefers them tied on shanks for the mobility. There are several reasons that help with the movement-
The shank could be weighted with dumbells to form a keel and keep it orientated.
The hook can pop out from the shank once the fish is hooked and the shank is then free to not interfere with playing the fish.
With the nylon running down effectively above the shank like a tram or cable car, it imparted more movement in the fly, whereas a tube swims a bit more rigidly.
The design really suits single hooks.
I have tied all my patterns on tubes as well as shanks and will be experimenting with both. Without sounding like a stuck record, I can highly recommend going to
www.aprilvokey.com and checking out the podcasts. The two part Jerry French interview covers the Intruder and then the development of the Skagit line and it is really worth a listen. I play them in the car all the time
Also check out any video by OPST on Youtube about the Commando heads and Intruder fly tying, and the
www.opskagit.com website. I really have a hankering for a Commando head for my 10' #4 Orvis Access!
Euan