These fancy suspensions look mighty good, but I wonder about their efficacy... I had a folding bike with rear suspension, it came with an undamped spring. That was rubbish, at a particular cadence it would bounce badly. So I made a bush from rubber to use instead of the spring and that worked fantastically. So to replace the birdy rear elastomer with a spring, even a well damped one... I don't see how this is an improvement in performance.

So the birdy comes with a damped spring in the front. The travel of this spring is maximised. Long travel is good - it is the best thing you can have for suspension. Basically, the spring force must change very little over the span of movement. The shorter the spring, the worse the suspension performance. A short spring will not absorb road bumps nearly as well as a long spring. This is very basic filter theory. So these fancy jobs look good but it is very clear that the travel is much shorter than the original spring. So again, I don't see how the performance is improved.

Sorry to be sceptic but it is basic filter theory.