I don't know if anyone has actually studied the difference in accuracy of a whisker biscuit compared to other rests. It seems almost everyone assumes that it is a little less accurate. Myself, my groups are as good with it, as with any other rest I've used.

I read somewhere that one experienced archer thought there might be some advantages to shooting through a rest that guides the arrow. Also, one of the major advantages of larger fletching or helical fletching, is the increased drag on the rear of the arrow, which straightens the front end out and gets it traveling in the right direction. I've often wondered if the biscuit contributes to this straightening because of the increased drag it applies to the rear end of the arrow, as the fletching goes through.

It just may be that the whisker biscuit is more accurate in some circumstances.