I've installed it on my Ibanez RG as a replacement for a middle spring. Was not sure about the size, it's really unclear which one to get (hint: S fits on RG with 3 stock springs and 9-42 strings, M - with 2 hard springs, L is probably to big to fit at all).
Works really well after oiling internal moving parts and replacing default tension spring with the other one supplied. Internal spring replacement is not so hard to do, as spring chamber is easily accessible (via small cap on the long end). Also I was really surprised with packaging quality, it even seems little a bit redundant, as you do not really need cotton pouch when Tremmory is installed, however it's nice to have anyway.