Good question, I'm happy to explain.
We spent a lot of time analyzing the ice skating stride with our research partners at the University of Calgary (Biomechanigg Sport & Health Research) as well as consulting prior research on the matter. The tendon guard on the Super Tacks skate is optimally placed to provide a maximum power stride. It has been straightened out compared to the previous version of Tacks to assure full clearance of the stride.
See this video from Hockey Tutorial on Youtube that illustrates this difference.
As for the tendon stiffness, it helps with its durability, as this is an area of any skate which is more susceptible to breaking down than almost any other part, due to how players put on and take off their skates. It's a spec that is often requested for our pro custom skates.