With a shotgun, you can comfortably go to a 4 or 6 minute dot - 100m is running up toward the limits of do-able, meaning you're covering 4 to 6 inches, which is still viable. I've always thought the EO tech reticle was awesome for shotguns, it was the rest of their units that didn't do it for me - but I've heard that Shield has some large circle reticles on their sights, so they might be worth a look.