I have a mk18 upper with A2 flash hider on it and I am finally getting around to changing mounts. Kids are starting to sleep some.
I have 3 mount options for this mk18 upper,
Dead Air Sandman-S I have a 5.56 flash hider, I bought two the other is on my PWS Mk107. (7.75 inch barrel) (does getting the 556 endcap really work better, I don't know but the Sandman is going to be 5.56 for a long time with me, it might be an investment.
Silencer Co SpecWar K I have one at home and another pending. I love that little can with a ASR Flash Hider, my Hybrid should be aporoved next month as well.
Or the old Standby the Gemtech G5 I have used since 2009/2010. I have some 16 inch guns I want to replace flash hiders to use my SpecWar K with. Its just the SpecwarK is 5 ozs lighter but will have extra mounts for the G5. Some no longer produces like the PWS FSC Gemtech device and Jake Brake.
My homegun right now is a LWRCi M6A2 10.5 with Gemtech mount but I am thinking of switching that to a Dead Air or SiCo to save weight. The Peq-15 and scout light and short stroke piston add weight.