It's popular in certain states that have limits on what you can use - certain states with shotgun only zones also allow straight wall rifle cases of certain dimensions. It was designed to work in AR15s, so the designers were limited by magazine length and strength of the action (max saami pressure is only like 38.5 psi because of this). If you handload I would assume you could go hotter in a bolt action though? It uses 452cal bullets not 458 like most rifles.
I live in a place with no restrictions on what cartridge I can use so it doesn't tickle my fancy as a hunting rifle, but I'd love one for plinking and fun. I prefer average to high sectional densities for hunting though. Id probably go for a 45-70 lever action if I wanted a 45cal hunting rifle as it has a greater potential and I could make loads that duplicate 450bush or outpace it.
As for velocity, the case is pretty small so I wouldn't think you'd be losing a lot with the shorter barrel.