Fleets use the fixed for several reasons. The fixed is lighter, stronger, and cheaper. Also, they don't risk Gomer crushing the reefer unit, or folding the front of the trailer on a tight turn. Gomer will do that, but with a fixed fifth wheel, at least he's limited to dangling the mirror, front bumper, and poking holes in any side fairing, and of course bending a rim or two, and tearing a back door off on a loading dock.
Some Companies haul the same freight, so their weight distribution is set. If you are going to haul different trailers, or different loads all the time, you want a slider.
I don't know the cost, but I can imagine those things are not easy to get off. :block:
When you shorten the space between the tractor and trailer, you will get better fuel economy. A slider can make the difference on some yards with real tight space, and save you from eating your own organs. I'll run long on some areas with washboard roads. It's more comfortable, and easier on my load. Even with smaller tractors, I like having a slider, because it offers me options.
When I got to use my first air slider...I felt like a top hand, even though I look like Gomer.