I have a Sig Romeo 5 on a number of my rifles. The shake on feature and the short interval auto shut off is great. The SPARC AR is good, but I just like the fast timeout/shutoff of the Sig better (2 minutes instead of 12 hours) and the auto-shake/wake to turn on more than holding a button to turn on the red dot. SPARC AR, though, takes a AAA battery, which is a huge plus. In my view, I like the Sig's more responsive click buttons over the more mushy Vortex buttons on their red dots.
Some of our sponsors have significant sales current on, for the Sig Romeo. I recently bought another for over $100 off compared to ones I bought earlier this year.
I don't know about anyone else, but I have my optic on the rail on the receiver, rather than the small rail on the removeable handguard. The rifle is so barrel heavy as it is with that aluminum handguard, I don't need to add even an ounce of weight more to the front of it.