Problem one: The sight sits way high. Of course you can get used to this.
Problem two: Sight-Barrel ratio. Not too much of a problem with bench/target shooting, but if you were to use your rifle for hunting, or CQB/combat type stuff, you will incur a problem shooting over barriers. Your head will be much more exposed so that you can clear the barrel of your rifle from the obstruction. It's enough of a pain in the ass with a flattop and an Aimpoint, imaging havint to go 2 or so inches even higher.
Problem three: If you think of how you are sighting, you are forming a triangle with your sight, the barrel and the POI. The greater the distance between the sight and the barrel, the more pronounced difference will be when you move the POI forwards or backwards.
Otherwise for the most part it works and depending on the sight, will look cool to boot. [:D]