I used flexwatt for a couple years, and towards the end of that I was having trouble keeping consistent temps. I did not think it was an issue with the flexwatt however, and thought the connections were bad. So I went onto RBI and ordered new stuff (which I thought was flexwatt but it was actually the THG heat tape) and rewired everything and threw out the old flexwatt. I threw out the flexwatt because the copper where my crimps were was very raggedy, probably from moving 3 times and getting tossed around.
So far have had no issues with the THG