Nim,
I bought a leupold RXII for the hunts last year. I mostly wanted a range finder for the flat open country of wyoming to hunt antelope.
I think it would work excellent for archery and muzzleload hunting, I found it very accurate and simple to use from 3 yards out to about 300 yards...
After 300 yards or so, it has a tough time "seeing" the animal or target ( bright or dim, live animal or not)that you want to read the distance of. The lighting has to be just right and the target quite plain for the range finder to do it's job.
On rare occasion it will live up to the 600 yard ranging as advertised, but only when the planets and stars align and the moon is in the right phase.
I don't know if all rangfinders have the same shortcomings or just the RX II. I also haven't had any other brand rangefinder experience to compare performance with the RXII.
Good luck, RVtrav