Are they worth the extra money?

Ive heard good things about them... but I use All american drive service and he makes his own as well. I would imagine they are comparable...

How much?

Any?

Do you have some? Know anyone that uses them?

My Max vert shaft, unlike the Teague, is still in one piece. And I've pushed it harder, I think they are worth the money.

I have used the Max "torsional" shafts with pretty good success, I have sheared 2 of them off BUT I logged over 400 hours behind my blower motors with these 2 shafts AND I have never had my upper blow up so there might be some truth to the claim that the torsional cushioning effect takes the stress off the gears may very well be true. The new owner of the Bravo shop is also marketing some very beefy looking shafts, Smitty

I have not had any failures when using the Imco vertical shafts, they are not as pricey as the Maxworks. I did install a pair of lower vertical shafts from Max once, but the lower pinion gear would not slide on the splines. I called and talked to the not so nice partner and he said, send them back. Well I was in the middle of rebuilds, so do I stop and wait for them? I ended up using a dremel tool with a diamond bit to clearance the splines on the shafts to make them fit. That is why I use the Imco shafts. They also have their own upper vertical shaft as well now.
Just my .02
Dick