I've had a Bushnell for about 25 years now. it is certainly worth buying for two reasons:

1. It'll save you a lot of ammo when you are first starting to zero in a newly mounted scope, or the iron sights on a new rifle.

2. When you travel to a hunting area, it is not always possible to fire a shot or two to make sure your zero has not changed, even though you should, if you can! However, if you keep records of where your scope's crosshairs are pointing on the adjustment grid of the borescope, you can slip it onto the gun and check to make sure the scope has not changed since you set it when you last zeroed the gun.