Been using my T6 for a couple of months now and touch wood have had no problems. I wouldn't say build quality is actually any less good than the Magicshine I have.
I guess one criticism I might have of the T6 is that there're only 3 modes - high, low, flash. The low is fine for around the city as a be-seen light, but no good at all out on unlit roads. My Magicshine on the other hand has high, medium, low, strobe and SOS modes and the medium is more than enough for most riding on unlit roads. But then it's really annoying having to cycle through so many modes to channge bewteen settings (medium --> high is 5 button presses). Ideally I'd like just the 3 modes of the T6, but with a medium instead of low setting.