I think they're a crock.
The ones that attach to the trailer coupler tube essentially move the trailer BACK relative to the truck, but when turned 90 degrees they move the trailer to the SIDE of the truck, i.e. the truck cab is just as close to the front corner of the trailer.
The ones that relocate the ball put the load behind the rear axle - just a BAD way to go, though they might save you a truck/trailer kiss.
BTW, it isn't the bed length that matters, it is cab to axle distance.
On US built "full size" pick-ups this is a standard 58 inches.
To get to 90 degrees you need the ball more than 1/2 your trailer's nose width from the cab.
A 102 wide trailer is only 51 inches from the side to the middle IF it is the full 102 at the nose, very few are.
Most taper to about 5ft., i.e. 30 inches from side to center.
Y'know, spin turns REALLY squirm the trailer tires and there is almost never a "need" to get into situations where the only maneuver available is a spin.