I recently swapped my M7 16% for an Alta V2 17%. I had alignment issues with the M7, it was eating belts and causing the belt tensioner to rattle.
I am very pleased with the Alta, the only problem with install was when tightening the interior bolt on the shaft. I have an 06' and the space between the shaft portion of the pulley and the body of the supercharger was very tight.
Anyway...
I have a few hundred miles on the Alta now, belt is in perfect alignment and the boost is consistent through the RPM range. I think the belt was slipping on the M7 and I was getting intermittant boost.

Buy one!

 

I also have my belt tensioner rattling... but only when starting the car until the engine warms up. And i thought it was due to the CP...