I just bought the kit for the 1100. I'm see many springs and seals, etc in the shop at work and these look great. Those guys at J&P are also really great to do business with. However, I did not think about what it would actually take to install the Hammer Spring and the Firing pin spring. The existing Hammer spring and firing pin springs in my 1100 work just fine. Taking that into mind as well as the difficulty of installing the two springs, I'll likely not install them unless one of the existing springs breaks.
However, the action spring was a snap to install. It does give a better feel to the action. I noticed that my original spring was slightly shorter and thinner.The J&P action spring is nice.
IMO, if I had it to do over again I would likely just do the action spring. However, if you need to replace the other springs, I say go for it.