Follow up on my comments. I just went back and hit the TS1, TS1-IM, the TS3 and the TS4 side by side with the same tour level ball. All #7 irons with the same shaft. I had done it a while back during development, but your question peaked my interest and I wanted to get a new feel (no pun intended) for each of the models. The TS1 and TS1-IM feel the same, to me. Soft with a slightly different sound than the TS4 and TS3’s. Not bad different, just different and I attribute it to the thin face and polymer injected designs of the TS1 and TS1-IM. The TS4’s and the TS3’s, again to me, sound more like a traditional solid forged carbon steel iron. I had several listen and some could not tell any difference while others could, so I guess it depends on what kind of sense of feel / sound you have. Whatever the difference is very subtle and does not take away from the fact that all the models, in my obviously biased opinion, feel unbelievably solid. Comfortable recommending any one of them to any type of player.