I’ll provide my insight. I played a TS1 set for 18 months. About 4 months ago I switched to the STi2. I am a 4 hdcp. While I was perfectly happy with the TS1, the GW custom shop was running one of their rare sales and I was interested in the STi2 built to my specs.
The TS1 look like a large blade, but don’t really play like one in the long irons. More forgiving than I expected. I did find toe misses to a bit punishing, but still better than most.
The STi2 is more forgiving in the long irons, but the short irons in the TS1 were more apt to be dialed in. I really felt like I could attack with the TS1 PW and GW. That being said, my GIR is slightly higher with the STi2, even though I have played and practiced a lot less in the 4 months with the STi2. Also, the sole of the STi2 does seem to be a bit more tolerable of ground conditions. Firm SoCal fairways sometimes did not agree well with the TS1 sole, but the STi2 handles them well.
Not much distance difference between the two. I did pick up 1/2 to 1 club length with the STi2, but that is more a function of 1/2″ longer and 20 gram lighter shafts. I recommend both heads.