The Cyclone GT and the Luxe VGT are both very good single-spring touring derailleurs..I've put many miles on both.
But....the best one I've ever used in terms of predictablity, reliability, and shifting to rival perfectly-adjusted Ergo, is the Huret Duopar. We've had one on our Taylor tandem for years, through many miles...I even used it with an 8-speed cassette for awhile...it didn't like the narrow cog spacing, but it did work. Use it with a proper 5 or 6-speed on-topic freewheel, and the Duopar is unbeatable... smooth and precise every time, especially with Simplex retrofriction shifter levers.
just make sure, as has been noted by others, that you don't try to back up unless the derailleur is perfectly aligned with a given rear-cog, or the chain will wrap right around the derailleur cage, or the cage will try to wrap itself around the freewheel.
The problem is easy enough to avoid, with a little care.
I'd never used a Duopar until 3 years ago, when we got our tandem, and I have to say I've been mighty impressed with it. It'll shift to 32 and 34 tooth cogs as smooth as silk. We have the titanium version, I assume the steel version works as well.
Charles Andrews
Los Angeles