Seemore type reflex sights emulate the kind of optics used by competition pistol shooters. These scopes have a dial adjust dimmer brightness control, the units themselves made mostly from polymer making them durable and robust yet very light. In the case of the rail attach version, the attachment bracket and plate is metal which adds a little bit more weight but at the gain of a much more durable rail mount.
They may be a bit exposed and fiddly for outdoor use (you do not want to go smashing this against tree branches) but indoors where environmental collision is minimal, the scope offers a nice big picture with low frame obstruction and low weight as well as mounting very low (closer to the bore axis).
Although originally designed with mountings for drilling on to a Hi-Capa type pistol, rail attach versions are also available and can find just as much use on railed SMGs and carbines. Powered by 2xLR44 batteries, two come included with the scope already installed. This model is available in various different colors.