They aren't kitemarked (but they are supposed to be in the process of getting a KM license for the 2,6 & 9l) but:
- The A, B, F & 35kV (electrical) ratings are independently verified by a French EN3 test lab
- The lithium battery claim is based on independent tests by the Swedish state laboratories
- The Class C claim is manufacturer only based on testing using the Australia/New Zealand test fire as EN3 doesn't have a test for Class C and assumes all powder extinguishers are suitable (but only powder. Note historically in the pre EN3 days it was not unknown for foam spray, CO2 & Halon extinguishers to be marked for Class C fires and some guidance supported it)
- The class D claim is manufacturer only and apparently based on the old German DIN standard magnesium test fire
It all depends on what risks you are considering it for - for many applications you can be assured of its efficacy, others you have to take it on trust with the manufacturer or do further research testing. I've accepted it for some applications, it's certainly better than powder for some traditional 'multi purpose' uses.
If you wonder what's in it - it's a bit like a liquid version of a powder extinguisher, having the same Ammonium salts as ABC powder extinguishers and possibly synthetic based foam (based on the patent and MSDS)