David Clarke 13.4s are excellent - I've had mine for yonks and would never change. I've got a couple of other headsets: they are now for pax!
I had Richard Holder convert the 13.4s to ANR, and that was a great improvement, too. HIghly recommended.
As supplied, they have the "foam" earseals fitted that make them weigh 13.4 ounces. Take those OFF and fit the gel seals - makes them heavier, but a lot more pleasant to wear for a long time.
They coexist happily with most other brands, but you may find sometimes that someone in the aircraft can't be heard or can't hear. Impedance mismatch: you just have to live with it.
Reliability is fine. Just watch the little microphone windshield, and the pad at the centre of the headband. Both mine dropped off and got lost - things aren't so good without them, and the price of a spare is ridiculous (the head-pad is something like £40).