I have had one. I found it quite good in that as soon as you start to burn, you can shift along it so that you are sitting more on the back of your thighs.
But, it has no springing at all and worse, the frames are hollow titanium tubes which are too weak. One day on Belgian cobbles saw one of my frames snap.
They may be less suited to ebikes where more of your weight is on the saddle and less on the pedals