I am now using a EoTech on my RRA FlatTop (mid-length). While it is a great sight, I still want a BUIS so I could change to iron sight when necessary. I am now pretty interested in a Troy rear BUIS (My RRA has a fixed front sight), and hear many good things about it.
However, I saw in some forums that when using the Troy rear BUIS, you have to get a higher front sight post instead of the normal one come with the rifle since the center of the rear peep hole on the Troy is higher that on a detachable A3 handle, and the normal front sight post may not be high enough to get a proper sight zero, is this true? If so, I will buy a higher post together with the Troy rear BUIS.
Does anyone have any experience with the YHM flip-up rear BUIS, I also hear good things about them, and the price is also attractive.
All BUIS have the same standard height.
I'm researching the same thing you are, and I've learned that while all BUISs use the same height, they are also all too tall for a standard FSB. This is apparently one of the reasons for having an "F" marked FSB.
I own a LaRue BUIS and plan on sighting it in with my normal FSB to understand how far off I will be. If it is a problem to zero my rifle, I will purchase the taller front sight post to correct the issue.
I'm told the difference is only 0.040", but I don't know how that translates at @ a 100 yard zero.