I need to install an instant electric shower with thermostatic control.

I have been recommended to use the Mira Advance 9.8kw (the largest thermo
they make.)

My initial plan was to use a Triton 10.5kw thermostatic (about the same
price as the Mira) but I was told that the Mira was a far better make, and
would give a comparable flow rate (for a given temperature) than the lower
powered Triton.

Give that;

1. I have to use an instant electric shower.
2. I have to have thermostatic control;

any thoughts/experiences/alternative makes please.

Thanks.