If your wanting irons (which its always good to have back up irons) id recomend magpul m-busopticsplanet.com/magpul-mbus-rear-flip-up-back-up-sight-gen-2.html or mbus pro, opticsplanet.com/magpul-industries-mbus-pro-flip-up-sights.html
If your looking at an electronic sight I'm a big fan of low powered variable optics, vortex makes them in all price ranges from the Strike eagle ($200ish)to the HD Razor ($2,000ish) or right in the middle viper pst gen2 ($550 used) vortex has the best warranty in the game too, even if you buy used theyll fix or replace you optic for life. They make a variety of reddots too, but i like the versatility of LPVO's

If using for plinking any iron sights or red dot. Home defense ide recommend a more reliable brand of red dot like vortex, burris, leupold, or sig sauer preferably one with a shake awake feature. Hunting/Truck gun a variable low power some in the 1-6x range. But everyone is different and this is just my 2 cents.

Hi Mike,
I personally prefer a red dot or variable scope for my AR. For variable scope, check Primary Arms 1-6x24mm. Primary Arms are incredibly affordable while being reliable. Honestly, for optics, I cannot recommend Primary Arms enough. Go check their site. Cheers.

inexpensive red dot I use this one budsgunshop.com/product_info.php/products_id/60657/truglo+red+dot+sight+w%2fmulti+reticle%2fdual+color

Mike, Iron or Optic? I have been using the TRUGLO TRUTEC RED DOT on my 10.5 inch and have been more than satisfied. budsgunshop.com/product_info.php/products_id/712014039/truglo+trutec+red+dot+2omm+blk+qd