Would a double action recoil spring be worth the $30 that my friend is offering me?? Are these double recoils are worth it. Please let me know what your idea and thoughts of this are for the Glock 21 Gen 4 DOUBLE ACTION SPRING?? If you dont mind let me know the reason why to install these. Also let me know if you think its worth it. Glocks are new to me and I could use your help to get versed on these bad boys.