OK, I'm back into this topic once more!
I'd been speaking w/Mark at LaRue Tactical about my problem of the SPR mount knocking into the rear BUIS and what to do about it, and he suggested a Totally different approach to the issue of 'iron sights', and suggested a JP point Micro-electronic Reflex Sight.  I hadn't considered these before as I figured 'electronic' was just another gizmo to fail when the chips were down.  
Anyone care to address this idea?  This will be used on an DPMS .308
Robert

Seems unlikely that both would go TU on you...unless you're taking it into combat, and I could envision plenty of things to cause them both to crap out.  

I'd get some type of irons because they're much more "bomb-proof", if you know what I mean.

Quoted: I am not sure how your optic is "knocking into" you BUIS? Got pics? Any duty/hd weapon needs to have iron sights on it. The JPoint is a nice little optic, but would not use it in place of back up irons. C4 www.GRTactical.com

Ditto on that.  Plus, if budget is an issue, the BUIS will be less expensive.  Get a low profile BUIS like the Troy or ARMS 40L, and have at it.

Sorry for not being clear in my description guys.
What I meant was not 'knocking into', but rather that, when both are mounted to the position that is right for me, they 'touch' together.  When they are back to back in this manner, I cannot completely throw the LaRue SPR's rear lever completely closed, so then I need to move the SPR forward one space on the rail which then becomes a little less than ideal.  My current BUIS is the DPMS Mangonel, and it fits well underneath the rrear of the scope and also works very nicely w/sight picture etc.
I think that you've basically answered my questions regarding Iron Sights vs. an Electronic Gizmo though; since this is my unit that I need to count on if all else fails, I'd like it as bomb proof as possible.
Robert

go with both

I refuse to own an AR15 that does not have a front and rear iron sights, no matter how many optics it has.

Quoted: I refuse to own an AR15 that does not have a front and rear iron sights, no matter how many optics it has.

+1

Quoted: Quoted: I refuse to own an AR15 that does not have a front and rear iron sights, no matter how many optics it has. +1

+2

No AR is complete without some type of iron sights!