Having played with one of those stocks (installed on an
M1A
) the other day, it was only slightly better than an M3 SMG stock for solidity. (OK it's actually several orders of magnitude better than an M3, but the theme is correct, torsion, side to side & up and down slop).
A shooter would have to consistently preload the stock in some way to have any repeatable long range precision; To my way of thinking, not a situation which could be consistently reproduced in the field...
From a machine rest , I'm quite sure that the accuracy of the individual rifle is increased by shimming the gas system and consistent free floating / tensioning the barrel. The system falls down in the butt stock.