They said you have better clearance, less to get hung up on, a solid surface to distribute the weight of an impact evenly along the slider, nothing to flex into the body, and no issue with torque on the frame, an easy install and for the few that care, easy removal for paint if that is ever an issue.
Just a few things to consider. Now those things may not matter to you or you may not believe any of them are of a concern, that's fine I'm not here to argue, its no money in or out of my pocket. I just want to point out the obvious which is great companies build products that have been on the market and in heavy use for a good period of time. You just dont find people complaining about damage from running good quality tub mounted sliders.
Whatever your choice hopefully it continues to provide years of trouble free service.