I took a spin over to IRUN's US site to look at both Gen 5 34 MOS FS and Trijicon RMR HRS, and boy is that tempting.
The only downside that I can think of is that if anything bad happens to either the gun or the optic, IRUN doesn't provide anything but a means to facilitate the return of the product to the manufacturer. They're not giving you a replacement while yours goes in for warranty work, they're not taking it back and sending you a new one - that's strictly not their policy. I would hope that the biggest difference buying at Rampart would be that if the optic went dead one afternoon, they would send you a new one and sort out the repair on their end. I would hope.
Bradley