Well, the HMR came out first...so it got all the rave reviews, and everyone rushed out to buy one.
Fast forward a bit, THEN the HM2 came out. It doesn't get as much press (or as much of a following) because of the already strong popularity of the HMR...what's so cool about a weaker round? It took a while for the HM2 to get noticed.
Bottom line...the HM2 is about 2/5 the price if you look around, so you'll save a lot if you shoot often.
It's still a little laser out to 100yds, is still capable of sub MOA at this distance, and is a BETTER choice for squirrel hunters. So for less money, you get very similar performance at typical rimfire distances.
If you don't plan to reach out past 100yds, or shoot anything larger than large bunnies and feral cats it's pretty hard to justify the added expense of the HMR--it just doesn't offer enough of an advantage at closer distances.
Personally...I choose the HMR. It's still relatively inexpensive to shoot and I like the extra velocity/distance for those longers shots--which is the only reason I even have the 17. I still prefer 22's for hunting.
The biggest problem with the mach2...
In my area, you can find ammo everywhere for the HMR...but coming across HM2 is quite a bit more difficult--and when you do find it, it's usually just one brand and only a handful of boxes.....meanwhile, the HMR shelves are over-flowing with a large quantity of brands and boxes.
I think it'll stick around a while as more and more 22lr shooters will move to the 17's.
17 rimfire ammo is of great quality--and the HM2 stuff is really not much more expensive than QUALITY 22lr ammo....
HM2 is a GREAT squirrel round!