The Master skates have been around for quite a while, just not for every mouse. They cost only several dollars more than the performance and competition skates, and come in a much nicer wooden box packaging. A bit unnecessary imo.
As far as the skates perform, they feel much slower than the competition skates which I find rather fast depending on the mouse pad you use. Those require some break in time. Not sure about the Master skates as im still using them. Im hoping they'll release them for more SteelSeries mice too.