Big difference and yes the extra cost is more than worth it. First off they are two different variants, your comparing the 226 to the smaller 229. While the MK25 is an excellent gun, it does not have the srt (short reset trigger) but that is an easy drop in if you want. Also the action on the da pull of the legion is much smoother and with combined with the srt is a much vastly improved trigger. The legion comes with the gray guns intermediate trigger along with the improvements I mentioned. The legion x-ray sights are much better than the sig ns. Better grip with the g10's, you have a better undercut checkering on the trigger guard, smaller controls, steel guide rod. While these are small differences, in total they are big improvement IMO and well worth the extra money.