I got one of those that TANGO has posted.
Had to modify the spring, threw it away actually and used a better spring, used a old spoke and hooked it up elswhere on the frame, and shortened or lenghtened for spring tension. Not too much tension, not too little. But the sring it comes with is rubbish.
The other thing I noticed, the swivel part, that needed proper attention cos the nut and bolt kept coming lose. You need it to swivel, and have zero slack tolerance. Not easy to do, but can be done.
But needs constant adjustments to take up the swivel-slack.
Needs to be bearinged for constant correctness. And the bearing replacable cos it does do alot of work and cuts the bolt in half. ( Every stroke of a 2-stroke, that swivel, works! )
Overall, it does not fit all frame types because it is clunky, long and bolty.
What is interesting to notice, the angles are correct, meaning when you pop the clutch, it works well. Someone did actually put some thought into it.
When riding, it is worth the hassle of getting it right because it just smoothes out the ride 90%-100%
Very smooth ride and less jolts, infact I noticed the jolts almost eliminated.
And the chain's palstic idler wheel hardly wore out in comparison to the fixed version.
Once I experience I properly set up spring chain tensioner, I don't want to go back to the fixed version.
But, each frame type may be different to set up.
I hope a better version and better looking version, within price range can be researched and manufactured, well worth the ride comfort.
Keep in mind the importance of that swivel section, use a bearing from my own experiences.