Some of these tube sights came with interchangeable apertures both front and rear. So you could adjust the aperture size at the rear, and the type and size aperture at the front. Other than magnification these adjust much like a long tube scope, but work like iron sights.
I've owned one Unertl tube sight, and a couple unknown maker's tube sights. Only restriction I've found is they don't adjust enough to shoot much past 200yds.