Hodge,
I have a Denny's "Nitrous Ready" unit...no problems yet!
Did you notice the guarantee they have? Pretty impressive huh? The salespeople were very helpfull, they even told me I didn't need the shaft I bought, they said I could have gone with one of the cheaper ones they sell but I figured if I go with the nitrous ready (their strongest one) I'll NEVER have a problem!
Also look into Mark Williams, I know a few people who are using thier shafts and, although a little pricey there real quality stuff. they have a website too.