They were lightweight and hi-tech looking, with a pilot valve operated 2nd stage. A little tilt valve operated the main valve that would gush plenty of air. The early ones had a metal body and metal internal pilot valve body that was in two pieces and screwed together. Next version had a plastic outer body which was actually ok and retained the same brass pilot valve body, which was not perfect, but ok except the air flow tended to flutter if you didn't breathe very smoothly. We sold 12-15 over a period of a couple of years.
The trouble that I ran into was with the final version in which the pilot valve body was also made of plastic, and the threads holding it together were a little soft. I don't know if many (or any other) catastrophic failures occured, but I experienced a total failure of one at 80' in Belize in about 1983. Said plastic pilot body separated explosively at the threads, also cracking the external plastic retaining ring, letting the whole second stage open up without any warning. That left a wide open path for the tank to empty in fast order. The sudden air expansion and the huge instantaneous cloud of bubbles were quite a surprise
I never dove with a Tekna again.