I have one from FT. It's my everyday device. My ONLY complaint is that the treads are just slightly short. With a flat top 18650 (65.2mm) there is 1 exposed thread on each end of the center tube. But it's solid as a rock and hits very well. The contacts will need a light cleaning with NeverDull or Brasso every so often to keep it performing at it's peak.
The button might have a tendency to unscrew. It's an easy fix by putting something in the female threads to take up the void and give you something to tighten against. I used bits of cotton (same stuff I use for wick) and kept adding until I could tighten the button down and have the correct throw.