I remember walking into a P-QS warehouse circa 2000, and seeing a half dozen or so cases of Slick 50 on a shelf, covered in dust. I also remember a few cases of QS HM with Slick 50 looking just as dusty. Not a big selling product out of the local distribution centers to the mom and pops. I don't think I ever sold more than a few cases of HM, and even then it was probably PZL. I'm not sure how QS HM sold in the big boxes, but enough to not give up on it. Just change the formula and name. Again and again.
IIRC the QSHM premixed with Slick 50 was not API approved. Not many HM oils at the time were if I remember. HM oils were "made for engines with 100-150k miles!" or something (way out of warranty)
Now apparently "high mileage" is 60,000mi and the oils are API certified.
Once they were a world of cool HDEO levels of zinc and boron and "proprietary seal swellers" and such. Now they're a really good way for oil companies to get just a wee bit out of ya lad. Marketing. HM oil is somewhere between a brands base (conventional/synblend) and their synthetic oil, some brands have HM synthetic.
Thats another price point, another spot on the shelf.
Its also a great way for oil companies to upsell you. 60k miles on some engines is just breaking itself in.
Engine technology is getting to the point where some vehicles are so light on oil that 10K ocis are common, filters are left on multiple times per some OEM recs, but at 60k miles apparently you need to spend a few more dollars because yeah, thats what it says on the bottle.
But yeah, per the OP, this classic looks good, probably has as much zinc as what was once our non API HM oils that was once common in these applications. Id think Delo or Rotella would be better and cheaper in some applications but if priced reasonably I could see it being a hit.