RHI,
The BYP would "see" targets it would give readings for as high as yours or farther, but with no easy way to check them I never relied on them. I never used any of the rangefinders on fur itself, but then few of them would "see" a small digger or predator anyway unless close enough that you wouldn't need the rangefinder for them anyway.
Most of my hunting was long range, not only for varmints and predators, but also for deer, antelope and often for elk and bear. So I really didn't need a rangefinder for predators or big game hunting with a lifetime of experience judging their range in the habitats I hunted them in.
Range estimation isn't as critical with the modern laser guided missile launchers most folks hunt with now days, but it was very critical while growing up using a Win 94 30-30 for all predator and big game hunting, and especially starting from the late 60's using handguns for a lot of my hunting.
So for me anyway, they did a useful and reliable job in the digger fields, but I probably never would have used them for hunting anything else. They also came in handy though when I set up my 1000 yard range with 1800 & 2500 gongs, and when putting targets out at other places to check sight-in or shoot just for fun.