Is it true I can only leave turbo mode on for 15 minutes at a time in the TK40?
I have a TK40 and i have left it on Turbo for a fair while (probably 20 mins or so) but i was outside, and it was cold, but certainly no issues. Didnt seem to heat up much at all.
Back on topic, i have the following Fenix's (i'll probably forget 1 or 2..)
TK10/11/20/40 E1/20 LD01 L0D (thats 8, i think thats all...)
Haven't had a failure yet. TK10 is my oldest Fenix, and suffered a fair amount of abuse i guess you could say, and its still going strong.
All of them minus the E1 have been submerged in water (just in a sink to make sure they are waterproof), no issues there.
TK20 feels to be the toughest, though its fairly new and hasn't even been dropped on concrete yet.
TK40 feels like its the weakest (other than maybe the E1, but thats tiny, so doesn't count) and that has been dropped off a filing cabinet (1-1.2 meters) onto concrete, and still works ok. I have written other stuff about my Fenix's in other threads...
So, in summary, Yes, i would say Fenix lights, particularly certain models such as the TK10 and i am sure the TK20, are reliable.