I had the 18" DDC in my cart at primary arms yesterday, I was really close to pulling the trigger, but I told myself I was going to hold out for the Ambi version. I'm always happier in the end if I don't compromise, even if it means waiting longer and spending a little bit more money.
I have been on the fence between 16" and 18" barrel, leaning more toward 18 as I already have a dedicated 5.56 16" spr type rig, and a 20" LMT 6.5 CM
The Geissele GFR 6 ARC sure looks like it does a great job bridging the gap between a small frame SPR 5.56 and large frame 6.5 CM AR