This is a good way to look at it. Believe me, manual stretchers, you can put 100% of your strength into a stretch and will only gain more. Stretching with not enough intensity will lead to crappy gains. The proper thing to do is start out gentle but consistently work up to your maximum strength. If manual stretching at 100% was dangerous there would be no need for the
LengthMaster.
LengthMaster users will attest to the stretch being far more than their own strength could produce. It is scary in the beginning and fear of hurting yourself is there but once you learn your way around this you will see the 100% intensity is not only safe but most effective.