I think it was down to the fit tbh, my first Systema rubber wore out after about 6 months, which isn't the greatest period of use from a hop rubber when you're as frugal with your ammo as I am.
But with that first one I got about the same fps as with a Madbull Blue, but still better results in range.
Then with this new one that I fitted recently, it's boosted it by 20fps. So it could've been that the fitment was wrong before or something, causing it to wear out faster than it ought to have done.
They're only £6 though, and how easy is it to change a hop rubber? You might as well get one anyway and give it a shot, I really rate mine.