The MBUS is a new back up “iron” sight that was introduced by Magpul.
First thought, the price is certainly right. They tend to sell for about $50 or so for a back up rear sight.
They are fairly light and they seem robust enough. Construction is primarily polymer. Like most back up iron sights, it features two apertures. They are adjustable for windage.
The only thing negative I have to say about it is I don’t like how the “ghost ring” is not rounded on the top like most metal rear sights. I am sure it is simply a personal thing, but something about it just rubs me the wrong way.
Overall, I would recommend it still, especially if you are looking for an affordable rear sight option. Well made and seemingly indestructible, like everything else made by Magpul.
UPDATE: Since this original wirting I have had quite a bit more experience with the MBUS rear sights. They are still a decent BUIS for the money, but I question their durability a little more.
This belonged to one of my brothers. He apparently tightened the sight onto his rifle a little too much and you can see the results. Magpul was very good about replacing the sight, which I expected from a stand up company such as theirs. However, what it says to me is that you might not expect the same kind of durability from this sight as you would from an aluminum one from a quality manufacturer. Gotta remmeber though, it is a back up anyways, not a primary. If you need a BUIS, the MBUS seems like a good value. If you are looking for a primary rear iron sight, I'd look elsewhere.