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.
If you’re wanting a comparison between the original TS1’s and the TS3’s, in our testing the TS3’s had a slightly higher trajectory and very slightly more spin than the TS1’s, which makes sense based on the actual vertical cg location. The designed lofts are very similar, either the same or within half a degree, so the loft influence on the trajectory would be minimal if any. Both feel great, but both do have a different feel. Hard to describe and is subjective, but in talking to one of our guys here who played the TS1 and now is playing the TS3 he said he thought the TS1 felt slightly softer and had a little different sound, contributing those characteristics to the polymer injected into the TS1. He also felt the TS3 may be slightly more forgiving, which goes along with the higher MPF rating it has. He followed by saying the TS3 still feels like a forged carbon steel head, which it is, just a little different than the TS1. Also remember, the ball you play has a major impact on the feel.
Hope this helps.