It's not really claiming a ten percent increase in strenght, in that is doesn't claim to be able to shunt your bench from 300 to 330 , or deadlift from 400 to 440 the first time you use it. What it claims to be doing is off setting the effects of muscular fatigue, so that you can eek out 11 reps instead of 10 etc.
I have not used it yet, and am unsure as to wether i will until I find out more about the product. It is also important to note that this product was not actually developed by Muscletech themselves, but rather by the University of Florida, Muscletect simply sell it.
The science behind the product seems sound, but it does lead to a number of question about changes to recovery times etc, as it is effectively allowing you to do more damage to the muscle fibre, and i have not heard anything about the product aiding recovery, merely fighting fatigue.