It is rated to detect heat out to 2000 yards. I've located deer and hogs well past 1000 yards and have no doubts about the 2000 yard claims. I've detected yearling sized cattle out past a mile. With the helion, you can see field mice on the ground at 500-600 yards. Now, can I definitively say that you're looking at a deer/hog/cow at a mile? No. With a lot of experience, I still need to be within 500-600 yards to positively ID before I even think about shooting. My terrain is relatively flat. A 100 foot elevation change is extreme.
I use the helion xp50 as a handheld unit to scan and identify. It's pretty high resolution and pretty expensive. For my rifle scope, I went with the trail xp38. It saved me about $500 or so over the xp50 scope. I figured I didn't need the bigger scope if I already identified everything with the handheld. Don't try to save money by just buying a rifle scope. Scannin with a rifle is a pain.