Product details - https://www.immersun.co.uk/

Installation manual - https://www.immersun.co.uk/wp-content/uploads/2019/11/immersun-installation-and-user-manual.pdf

This product has several modes (all set using software)
- Power 1 element

- Power 2 elements (first is priority)

- Power 1 and a tank De-stratifier (ie stirring pump)

I used in it to heat 1 element and run a destrat pump - it works fantastically well.  When I have ample Solar PV, I get a full tank of very hot water for free.  See install guide for wiring.