Doesn't really matter which you keep as long as you replace to end up with a matching set. If I had to get rid of one, it would be the Matech rear. Matching conventional MI AR sights are probably easier to sell later. Ultimately, I would get rid of both and replace with Troy Micros as they are shorter and work better (to me) with the XCR. Not all faces and cheek welds being the same, standard AR height sets may work better for some.