Tungsten is much more dense than stainless or carbon steel, so putting tungsten in the toe, or anywhere else, allows designers to move the CG more with less mass. Totally depends on the design and whether or not it would be beneficial to use tungsten to help manipulate the location of the cg, hopefully for the benefit of playability. Generally speaking, lower locations help lower the cg. A low / toe location would help move it farther from the hosel and lower, etc. I think you see it being used more in “Players” irons because they generally have shorter playing lengths, narrower soles and longer hosels, none of which are elements of design that increase playability. If you can add tungsten to the lower toe and possibly a little rearward on these type of designs, you can possibly get the cg in a better place, improving playability. That being said, some of the modern “Players” designs are so small and have such long hosels, you can’t locate enough tungsten in them to make a big difference. It has to be a combination of the optimum dimensions AND the proper amount and placement of the tungsten to maximize the stability and ultimately the playability of any given design. Some designs won’t need it if the mass and dimensional characteristics accomplish the goal with out it. We don’t do it just to do it because it does add to the cost. It has to be beneficial and improve the playability or it’s a waist of money.
The TS4 and the MMB-17 will be different in their appearance. Although they are both “blades”, you will notice the topline is slightly thinner on the TS4, the sole is slightly wider on the TS4, the toe shape is slightly different on the TS4, the finish is different, etc. Neither could be mistaken for anything but a “Players Blade”, but they will have different looks and specs. The TS4 will have stronger lofts – 29.5 on the #6 iron vs 31 on the MMB-17.