I ordered a Trijicon SRO way back when, just received it and immediately mounted it on my trusty USP Expert 9mm and report the following: it is clearly easier to pick up the dot with the modified window. From low ready the dot starts to coming into your lower peripheral view at about half way up on your presentation. If you use the punch out technique to gain your sight picture, this will probably be even better. I am using the 2.5 dot version. I like the set up tremendously.
I like the looks of the SRO but is it possible to use your back up iron sights if it fails? Does it mount where the rear site would sit without modification to the slide?
No, you must remove your rear sight to use the EGW mount. It takes a good sight tool to install the mount. I can't justify cutting on a righteous gun like an HK Expert. I figure if the sight goes down in a gunfight, I will go CQB and beat the adversary to death the the pistol. Or use it like a boomerang and aim for the head while I go for my back up.