I have one for a 9.3x74R double, and have found it ideal for big game from very close to about as far as I have wanted to shoot with that rifle. It is very light and, having fewer lenses than a variable, passes plenty of light.

I also have found a 4x ideal on a .22 LR for rabbits and such.

I had one on a .45/70 too, where again it suited the use I had for that rifle. The magnification was ideal, with no need to fiddle with it, and it had the added bonus of a small eyepiece diameter, so it could be mounted good and low without obstructing access to the hammer.

Plenty of reasons to like them.