The flow rate without the valve was calculated through the valve and not through the shower head. I removed the ceramic cartidge and checked the flow through the valve. However before doing this, without the DCV I checked it running through the shower head. It did the same as before, started flowing, but reduced to a dribble. I assumed that this was then due to the hot water cut off valve kicking in.
In relation to the flow the MIs indicate that with 1m of head on hot, at 1.5 bar cold, at 65 degrees hot, you would get 8 litres per minute.
Not great, but it works and when used was ok, similar in level but a bit better than the aqualisa electric shower in my office.
I guess I might have had the same effect with a standard thermo mixer, but it works anyway.
JA