Before I start, I must make it clear that I do not work for, or have any direct affiliation with any manufacturer of fire extinguishing equipment, I am, however, a customer of many differing manufacturers, as in my business, I focus on providing the best solution for the job rather than the cheapest solution.
The time has arrived, once again, where I must question the validity of our friend Mr Buck's title "Fire extinguisher expert", when he clearly does not have a clue about this subject of this thread, I'm not saying he shouldn't hold that title, I know he is very knowledgable in many areas, but in the role of an expert, IMHO, facts should be portrayed, not personal opinions, especially misinformed opinions.
In reference to the use of "wets" on live electrical items, the clue is in the title, DRY water mist. Now I know that may seem like a contradiction in terms, but when the medium leaves the business end of the hose, that is exactly what you have, a DRY water mist. Furthermore, I would have expected our "expert" to have known what was actually contained within this type of extinguisher, before misinforming other users of this forum who may rely on information provided by an "expert". Many references to other manufacturers water based extinguishers have been made on this thread, and, under many circumstances those comments would be valid, if this type of unit contained water, obtained conventionally, from a tap. The unit in question, however, does not contain tap water, it contains demineralised water, which has vastly reduced electrical conductivity than ordinary tap water, therefore making the unit in question completely safe for use ON live electrical equipment.
Have a look on YouTube, and you will see some very impressive videos from the manufacturer of this unit, (that is a clue for what to search for), you will see this type of unit used on several classes of fire, including direct use ON live electrical equipment.
My personal opinion on this unit is that it could easily be the future of portable extinguishing, and OK, the B rating is low, but in general day to day life, how often are fire extinguishers supplied for B class risks ?