My father bought one of the H&R 450s back when they first came out, and he loves it for close range whitetail hunting. One reason he likes it so much is because there's usually no tracking involved
I've shot the rifle quite a bit myself and the thing that suprised me the most was the accuracy. H&R/NEFs commonly produce good accuracy for being a cheap gun, but usually not outstanding groups. On top of that, a straight-walled cartridge shooting a big blunt-nosed bullet usually doesn't result in amazing accuracy. However, I was able to print several 1.25" 3-shot groups at 100yds with the gun shooting the Hornady factory ammo with a 350gr JFP. Of course 1.25" groups aren't spectacular, but that's a heck of a lot better than the 3"+ groups I was expecting when he bought the rifle. Maybe he just got a good one, but if all of them will perform similarly, IMO it would make a better choice than the lever guns in 450.
As for the 450 cartridge itself, I like it, but it can't do anything a hot 45/70 won't. Truthfully, for a reloader, there's little use for the 450. However, for those who must stick to reasonably priced factory ammo (not Buffalo Bore and such), the 450 makes a lot of sense.