Easily the best back-up sights i've ever used. - Magpul Industries MBUS Pro Flip Up Sights

I've had good success with Magpul's ubiquitous polymer MBUS sights in the past, but when I put together an SPR build I decided to go with something a little more solid and usable so that I could take off my optic and use my irons regularly and at serious distances. I wasn't entirely sure if the big price jump over the MBUS's would be worth it, but all my fears were alleviated the second I opened the package. These things are build like tanks, and packaged far better than the lower-end MBUS sights are. I'm really glad I sprung for them. They work great. I paired the MBUS Pro front sight with the MBUS Pro LR rear sight that is fully adjustable for range just like a standard A2 style rear sight is, and they work great.

These are more than just backup sights; they're great sights in general. If you want to really use your irons and not JUST have them there for backup, I can't recommend these enough. Don't let the high price deter you. They're a truly premium product.