I used it once and it seemed fine to me. I would point out that SUperTech HM oil is one of the very few (if not the only one) of the HM oils that also meets the Energy/Resource conserving standards.
My theory on this is that it's more marketing and less High Mileage oil that we typically think of. MAG1 (WPP's retail brand) of Synthetic Blend oil looks the very same as ST HM oil (down to the red bottle) and it also says its "Formulated for high mileage engines". So perhaps it has some group III oil blended in with regular ST and also a little more seal conditioners, rather than being "thicker" and for whatever reason Walmart decided to market it as High Mileage instead of Synthetic blend, but it's really both.
Just a thought.....Whatever it is, i think it's a decent product and i'd have no issue using it. I'm not sure it's worth the extra $ over regular dino SuperTech however.
If you google MAG1 you can check out their website which has excellent data sheets on the oils they sell.