There are differences however including most notably more adjustability in the form of Titleist’s SureFit CG technology that allows for more specific spin rate and launch angle tuning. The TS3 also features a more traditional pear shape and tends to produce more of a mid-launch as compared to the TS2’s higher launch.
Other features of the new Hot Metal include the aforementioned “stability frame” design for higher MOI and improved launch as well as Mizuno’s new Pearl Brush non-glare finish.
Putters with more forgiveness and stability like larger mallets typically provide superior distance control because they maintain consistent ball speed and roll even on mis-hits. Unless you’re exceptionally accurate with your contact point (repeatable impact in the center of the putterface) don’t fall overly in love with the more traditional head shapes.