For the record, when most of us have been discussing shooting at both 100 yards and also at 20 yards, we are always using the product you saw, which is the HHA Optimizer Speed Dial. This is the only product of its type and it's also the only way to take the guess work out of being exactly on target at all distances.
Using your scopes MOA's is an approximate at best, depending on what distance you are shooting. You might find certain MOA dots that line up with a given distance, but other will only come somewhat close to other distances.
The HHA Optimizer Speed Dial allows a shooter to forget about using the MOA Dots and use only his center crosshairs dead on center at any distance from 20 yards to well over 120 yards or as far as you want to sight it in for.
Len and Andy Backus carry and sell them as distributors for HHA or you can purchase one elsewhere if you choose.
I've written an article on how to best optimize these units on your crossbow, so if you look back in the TAC15
/ 15i articles in this forum, you'll find it.
There's a night and day difference between shooting with one versus without it. It adds extreme accuracy in 5 yard increments and takes all the guess work out of calculating which MOA is for what distance.