What is the eye relief like on this optic?  Would it work on a traditional type rifle setup (M1a) or would the eye relief be to short for that type application?  Is it fairly inline with the Trijicon ACOG and Primary Arms prisms eye relief wise where the eye relief is rather short?

Our 2.7" eye relief falls right in line with other prism optics on the market. A short eye relief is just inherent to the design. Primary Arms lists their 5x prism with a 2.5-3" eye relief which means ours falls right in the middle. As far as what you can put it on, the Spitfire 5x is rated for just about any recoil you want to throw at it. It really boils down to how good you are at managing recoil. If you have a muzzle brake on the gun and it's pretty easy to manage, you could absolutely put one on there, but if it's a lightweight rifle without a muzzle brake and it jumps pretty good, then you might want to shy away from this optic as an option. Let us know if you have any other questions and always feel free to give us a call as well at 1-800-4VORTEX ext 1.

I have a couple of 5x.  The eye relief is very similar to an ACOG TA31.  You'll need a very small (front to back dimension) flip-up BUIS if you want one behind the Spitfire 5x Gen 2 HD, because the optic needs to be in the second the rear most 1913 slot (or the rear most if you don't intend to use a BUIS).