It seems that the -4's were all over the place regarding use on MIM parts or not. I have a -4 with no MIM and the old style cylinder release. I have a -4 7 shot 2.5 also with no MIM and old style cylinder release. I had a -4 2.4 " with old style cylinder release BUT it has MIM trigger/hammer. I would suspect the a lot had to do with using up old inventory. The -4 is the stopping point for me simply because I did not like the cosmetic changes to the -5 (leaving aside the MIM issue). I never warmed up to the new style cylinder release, cylinder stop lug or the frame mounted firing pin. To me, centerfire S&W's just look better with the hammer mounted pin. And at my age I have earned the right to be opinionated over stuff that really doesn't matter
