I bought the shaftmasters for my 2010 Automatic..and never installed it. After reading a lot of horror stories, the shaftmasters on 2010 auto's was a bad combo. Tweak the pinion angle all you want, and folks could never get the vibration out. A buddy on the roush forum also has a 2010 auto...and after a lot of tweaking, finally got the vibration to vanish...or so he thought. He had it up to 120 mph, and presto, vibration back again.
So sold my shaftmasters to a local buddy with a 08 manual..and zero problems for him. I bought the DSS, and it comes with a CV joint at axle end ( my shaft masters didn't). Pinion angle is non critical with the DSS....since it has the (replaceable) CV rear joint. Put it on the dyno..and wound it up to 150 mph in 4th gear ( 6 krpm, 3.31 rear gear, and 27" tall rears). Zero vibration at 150 mph.
Have not touched it in years. Rated for 900 hp, and is 3.5" OD aluminum. If you are paying somebody to install it, you want plug and play...not endless additional pinion angle tweaks. Even if you do the install yourself, the endless pinon angle tweaks are a pita. The best that can be done is to shift the vibration up to a speed that you will never encounter. After hearing the endless gong shows my buddy's were going through, I thought it prudent to just sell the shaftmasters..and buy the more expensive DSS.