I can't speak for the Leupold.I bought a Trashco Shot Saver and it was or is plain garbage.I'd have it dead on. I was lucky to keep it on the paper.Boresighter's get it close ,but as you said you'll still have to shoot it at the range.I don't think I would buy another boresighter.I would rather shoot a few more rounds to get it on.
Ruger Redhawk

..... A Proud NRA Life Member since 1977 .....Ruger Redhawk