Have you tried it upside down?
OK were not upside down much
My only concern about the present unit is the difficulty in obtaining and the cost of replacement diaphragms. The reg breaths very wet if its inverted which is a surprise too.
I found the WOB on the present unit to be comparable to the standard KISS unit.
ATB
Mark
You can get just replacement diaphragms from Interspiro UK for about £20 I think. Looks like a PITA to replace though. The diaphragm assembly looks to cost in the region of £48+vat