I'm an owner of an old double Iron Cobra HP200 (the so called Jr. Iron Cobra), and it has served me acceptably for years. It's not the best pedal in the world, but it was the cheapest brand name double pedal I could afford at the time I bought it. No major problems with it over the years, but in time the little plastic washers that the spring attaches to got worn out, and I needed to replace them. Found a replacement easily enough, but (fortunately) coudn't get the delivery to my country. I then looked up some equivalent on Thomann, and found these babies. I guessed from the picture that they should fit (couldn't find exact specs), and ordered a pair. Installation was super easy, and the result is incredible. When I tried them out it felt like I had been playing my pedals under water for years. The force needed to get them moving was so much smaller that I had some trouble finding my balance at first. I also needed to get used to the response time, which was much quicker now. When playing, it felt like I was rushing with my kick all the time.
I quickly got used to the new feel, and now it's easier than ever for me to play the kick. I also gained some speed. One more important thing is that it is a lot less noisy (practicaly silent) - something that was always an issue with the previous hook attachment system.
Pros: less force needed to play, quicker repsonse, no noise from the spring - drastic improvement of the pedal mechanism
Cons: it takes some getting used to the new feeling, but this quickly fades away, and you end up with a significantly better piece of hardware.