I purchased an LCDVF loupe for my D800E and can say, Scott Oberle’s reservations are well justified. The use of a RRS L-Bracket does definitely interfere with the LCDVF’s frame which snaps onto the D800 in the same fashion as Nikon’s standard LCD protector. I solved the problem by cutting a piece of cardboard (min. 1.5 mm thick) slightly smaller than the base of the L-Bracket, adding a hole for the screw, and then fastening the L-Bracket (together with the cardboard spacer) to the D800 in its usual position. This helped to clear the small lip at the base of the LCDVF’s frame, allowing it to rest securely in place. Interestingly enough, I never had such problems with the RRS L-Bracket in conjunction with Nikon’s standard LCD protector. However...!
If you have poor vision and wear glasses, as I do, you might incur considerable problems with the LCDVF ‘4N’ (the version made specifically for the D800/E) because of its lack of dioptric correction. I have progressive corrective lenses which make it extremely difficult to use the loupe. If I use my reading glasses, I have no problem at all. However, the ‘reading’ portion of my progressive glasses is at the bottom of the lenses (logically enough) which makes use of the loupe literally a neck-breaking affair! Just a small warning for potential buyers.
P.S. I believe only the LCDVF '3C' (the version made for Canon's 5D MkIII and 1DX) offers a diopter correction option.