Apparently, McDavid absolutely loves this specific type of sock, and even after the equipment company discontinued making them, McDavid refused to find an alternate. Instead, he insists on using the socks as they fade away.
It's a similar ritual to what Patrick Marleau endured, who became so accompanied to a brand of skates, that he bought out the remaining stock and used them for years after they were discontinued.
There's no questioning of whether the socks work though. McDavid's career offensive statistics are already insane, and he's currently posted 33 goals and 76 points in 41 games this year - on pace for the best year of his career.