The Ripstop was one of the last so called "bikini" tools to be made. It and the Evo (virtually identical tools) were released the year before Gerber decided they didn't want to continue that line, and I am sure they were not made in the same numbers that the others (Resolve, Suspension etc) were produced in because they weren't made for long. That is most likely why they seem rare.
As for what's special about them, the answer is simple. Nothing.
Def