My understanding of the pen spring thing is that they are removing the pigtail, which doesn't do much by itself as for weight reduction, then removing the inner spring on the strut, and installing the pen spring as a filler so the larger OD heavy spring doesn't kink, while keeping reliable reset....the gun can function for many by removing the pigtail and the large outer strut spring, but enough folk had problems with reset that the stiffer outer spring was left in place with the pen spring filler installed...

Or any permutation you can think of with these....which is fine for a range gun, but begging a gun firing when not planned otherwise, as far as a carry gun...most folk doing these mods don't know of the problems Glock-type guns have in firing unplanned...they don't know the Glock manual of arms includes having a rigid holster which completely shrouds the trigger...and the S&W Sigma manual doesn't have such a precaution as the design does not require such....but modify the gun, and it surely does, but they do not know it...kids playing with matches