What is the attraction to this upgrade? What do you gain from it? Just asking because I don't know anything about them. Is there anything wrong with the stock ones?

The stocker is a 2 piece shaft and weighs quite a bit more, more rotational mass. If your going with lots of power upgrades they are rated for more power as well.

Also found this for you new v6 owners! Upgrade before you take the speed limiter off!

Found this as well.

http://v6mustangperformance.com/news...haft-failures/

The reason I was thinking about changing it was that I have heard it gets rid off some of the clunking in the driveline with a manual trans. The weight savings & rotational mass, I really don't care about.

when it went I actually jumped lol

I've been hearing about these v6 shafts blowing apart. Not good.

Ah yes, the clunk... The driveshaft helped with that (quite a bit actually), but it is still there. There are also "anti-clunk" washers/shims available for the front bolt of the upper control arm, but I found that made little to no difference.
If you do consider the shaftmasters unit, there is a space for a coupon code in their checkout. Until the end of the month, entering "SANTASHAFT" in this space will net you $50 off the price.

nice savings^^^^