A slider hitch allows the pin to shift towards the rear bumper which can be helpful when maneuvering in tight spaces. It can be most beneficial when the distance between the rear axel and back of cab is reduced, typically with short bed configurations.
The manual style requires someone to exit the cab and release the hitch slide lock. The automatics do not require a person to release.
Only you can determine what you need. What are your driving and maneuvering situations going to be?
I had a friend with a Dodge short bed and a manual slider. On 2 separate occasions he forgot to release the slider, damaged the cab rear pillars both times.
I had a 2006 Megacab. I chose to go for the 24K pricey one. Never had to worry.