I just installed the laylax 210% spring. The spring is longer than the 170%, stifness seem the same. Installing it is tricky and hard because the spring is so hard to press down while installing the taper head. It took me a few shots and had a little hurted hand after. At this stifness use caution.
This spring is very hard on the arm to cocked, and after 10 shots, my arm was really tired (I'm not the muscle type). Power is incredible, very hot, and the accuracy seem better, wich is weird. Goes through both side of a can at 10 meter distance, and also goes through a cardboard box (where I put my energy can in).
I am disassembling my cylinder each weeks to see for wear.