I'm about to use Dyathonite Thermactive on a barn conversion near Leeds - being applied by Jordaya Contracting - at about 60mm thickness.
Our architect took us up to a property near Grassington who had used it and they didn't see to have any issues drilling into it to hang things. Ecological Building Systems also sent us a sample piece which we played around with and the finished product seems pretty solid, at least enough to hang a shelf off although you will end up with a bit of a thermal bridge.
On the breathability of the paints. I was in a similar conundrum and reluctant to go down the clay/ lime wash options as a lot of the wall will be in an open plan kitchen, and we want something washable. We think we will go with Beeck Mineral Sillicate paint, at least the stats look good.
Diathonite should be going on early Jan so happy to share any feedback post then if you wan.