I tried an Eotech on mine first and when placed where I <span style="text-decoration: underline">thought</span> I wanted it ended up cutting the piss out of my thumb.
I mounted a DMS directly to the factory rail with a set of Warne rings (low's IIRC).
These pics were from a 'what sling' thread. Let me know if you'd like a better one and I'll snap a few and post them up.
I can't really think of anything I'd change. I really love the rifle. I've used it in some 3Gun and Tactical Carbine matches and it rocks in the CQB stages. Especially in a 3' wide hallway with windows to either side. Instead of having to lean back to clear the walls I basically just moved forward and pivoted left to right. The muzzle stayed 'inside' the window so the blast was impressive but you can't beat it at being a handy OAL.
The only problem I had was the three allen head screws holding the factory rail in place worked loose during a 3gun match one day. I fired like four or five rounds at a 50yd plate before I realized the rail, rings, and optic were moving around on me. I had to remove the scope to get to the screws, apply a little loctite and re-mount/re-zero the scope and it's GTG.
Not optic related, but if you buy a STG (or any AUG style for that matter) look into the Trigger Tamer. I cannot recommend it enough. Being a bullpup design the factory trigger is crap. The Tamer cut it by about a 1/3. It's by no means a massaged AR trigger but it made a huge difference! http://www.triggertamer.com/