The 'device' you speak of is junk from all I have ever heard, thought I've never owned one. The only laser rangefinder I have ever used is my Leica 900. It is very easy to use, has great glass and the read is instantaneous. I think most rangefinders are rated based upon there ability to measure distance off something like a reflective road sign. Their ability to measure distance off a deer is in the neighborhood of about half, maybe a little more, of their rated distance. That is, my 900 yard rated Leica is probably good to around 450 to 500 off a deer. Further than I would likely shoot. A 400 yard rated rangefinder will not give you readings off game at that distance. Check out several different models before you buy.
