I disliked the Fly rope when it came out for the same reason (bungee cord qualities). Although I did buy a 150' hank and climbed on it for 3-4 months before realizing how much I disliked it. They still got my money though.
The Fly rope went through several incarnations in its first couple years. The one I have is from the first 6 months on the market, and it was much stretchier than Blue Streak. The Fly rope you buy today is different.
6.1% stretch is not acceptable for a tree climbing rope! That would be a tiring PITA trying to climb that rope.