The new TS2 features several design elements that contribute to making it significantly longer than the previous 917 D2 including an extremely thin titanium crown that’s approximately 20% thinner.
Aimed at low-handicappers and pros the 919 Tour model replaces the 900 Tour a.k.a. the Brooks Koepka model and features an improved shape with a bit thinner topline that the many Tour players who game the iron prefer. A new more durable Pearl Brush finish reduces glare while providing a bit more refined look than the previous matte finish.
Check them out and see if one is right for you but keep in mind the TS2 is aimed at those who want high launch low spin distance and forgiveness while the TS3 is aimed at those who want mid launch low spin and enhanced workability.