They work if that's what you're asking. I guess whether its worth it depends on how many additional times, if any, you'll be recalibrating your speedometer. Not something people do often. How many times, on average, do you change tire sizes on each truck you've owned in the past?

 

I'm thinking that my new summer tires will be 35" and my existing "winter" tires are 33". So twice per year I'd use it.

 

Depending on your YMM, you probably better of with a tuner. I know Jet makes those for GMs, but I haven't dealt with them on any fords. I have once fumbled with superlift tru-speed. Either way, it is a box that takes the incoming dwell sign and changes it to your desired dwell.

I don't know if it's bothered anyone else, but it took me 5-6 recalibrations to get my BFGs as accurate as they are. Against my GPS, I am finally under 2.5mph off at 60mph and dead on around 35. My tires are supposed to be 35" they measure just over 33 and 36" is what I am using for my tuner.