The creeper drive is a true underdrive, i.e. it actually changes the gear ratio at the drive shaft input. Therefore, you keep the standard 3 speeds and reverse that you already have, in High range on the creeper drive. When the creeper drive is in Low range, you have 3 lower gears than your standard 1st gear, and reverse is significantly slower than the standard reverse. Unfortunately, that's one of the downfalls of the creeper drive, the low gears are great for going forward, but it would be nice to have reverse as a standard speed. I've found this true when using a snow blower and trying to turn around in the street or back straight up to take another pass with the blower. I actually would shift back into High range then shift into reverse and back up all the way to the garage for my next pass. Then drop back into low gear range and 2nd to go forward with the blower.
Everyone will agree that the creeper drive is a MUST for a snow blower or tiller. Otherwise, most anything else that you do, standard 1st gear is plenty slow enough, and gives more than enough power to push, pull anything that you "should" be doing with the tractor.
1951 Farmall Cub, Cub Cadets 102, 104, 1811, 1864, Simplicity Legacy XL 4x4 Diesel with FEL, 60" mower, 50" Tiller