I don't know much about Joseph Rider or the gun you're looking at. I know he had Remington build one or more guns of his design, but I don't know if or when he went to work for Remington. The Rider gun I've always wanted - but not $3k worth of want - is this one, a .32 extra-short, 3" octagonal barrel magazine pistol. Sort of like a deringer with a tube mag.
www.horstheld.com/0-Remington-Rider.html