To fit any kind of recoil reducer device you need to cut the stock down by the width of that device which sounds obvious really. People don't like doing this on the better grade guns especially as they perceive a loss in value and they may have a point, on the cheaper sub £2k stuff it's a no brainer as it will not hurt values but if anything make resale easier. Why people live with the fatigue is beyond me.
I've had nearly all of them and they work, the adjustable ones are better as they can help you get rid of the unwanted shuffle effect which can occur when set too light. If you really want to avoid altering your stock then buy a PFS which is the best, most adjustable and a completely separate unit. :wink: