I have operated our sled CAFPC for thousands of hooks over the years. You can see it first hand from there. Watching the speed on Ag-tronics. The guys with the devices are able to hold a speed a tenth or so under the limit. Without they are normally 2-4 tenths under being careful. Sled pulling has a lot do with how fast you can go at the end of the pull. Sometimes a couple of tenths can make the difference in a 6" victor or loss. These devices are for sale and anyone can own one. I personally don't care. I don't have one as I like the challenge of staying under without the use of one. But this is what I have seen from a sled operators view.
Thanks, Leroy Nurenberg