I may have added a little confusion in my post. I call the Aber Halo a riser sometimes,i dont use a riser and the Aber Halo. Just the Aber Halo. Plus i have the advantage of being able to move my bars forward more. It feels very rigid in comparison. Actually even without the Aber Halo the S-type bar stems are slightly more forward giving one more cockpit room. Of course one can move the saddle back more but that doesnt place my knees over pedals as i like them to be.
I found the flex seemed to be mostly in the M bars bars themselves when i test rode a M bike. Probably why they sell the brace for M-Types as there bars seem to break eventually, from flex i suspect.
Also when i gave the 39 1/4 inches figure that was a estimate if the Aber Halo was straight up and also that was from the top of bars as asked for (i usually would measure to center of bar tube),mine is slightly forward which puts it still a inch or so lower than the M-type according to Bromptons figures which i just looked up
No offense to M/P type owners meant. Hope this clears things up and my ride feeling could be subjective re: flex, for sure.