Had mine installed by Solar and Electrics Worscester last Friday when my PV system was installed.
I ordered the mk3 2 weeks before the installation and was told it would be with me, the day before it hadnt arrived so I called and spoke to a helpful chap who arrnaged to sent it next day before 10am. I do believe they have some issues in getting the units out the door !
Looked quite straightfoward to install, although Tarum had installed the unit before.
It works very well, so well my water is too hot, limited control on the immersion element. I added a Mangers tank jacket to my foam lagged tank and its still very hot in the morning before any production.
I do have a issue that the lcd display goes blank and can scroll odd letters, reported this and waiting for a replacement unit to be sent out. I hope I was just unfortunate, but Dan from SolarImmersion has been helpful so far.
Would I recommend the Solar Immersion mk3, yes I would, no flicker issues like the Immersun. My only critism is I would like to see how much is being sent to the immersion, ie today 4.5kw.