Yes they are. Just like every water based spray extinguisher in Mainland Europe is and has been for decades. Just like they even were in Britain when first introduced until it was seen to be not the done thing (nothing to do with any actual incident)
The extinguishers are marked as safe for direct use on electrical fires up to 1000V in accordance with EN3, the European Manufacturing Standard (the pure Euro version, not the UK version) for fire extinguishers and the manufacturer, Britannia Fire, is fully prepared to guarantee their product safety.
Whilst BS5306-8 does suggest that premises should install CO2 extinguishers, it is only guidance and is written with heavy input from the extinguisher trade and many clauses are not evidence based. Most mainland European extinguisher provision codes and implementations of EN3 support the use of di-electrically tested 'wet' extinguishers for direct use on low voltages (i.e. under 1000V) and there are no known cases of electrocution from approved extinguishers - historically electrocution cases date back decades to the use of soda-acid extinguishers (discharging powerful electrolyte solutions) and more primitive electrical installations without circuit safeguards.
Many large concerns have switched to a single extinguisher type (Britannia Triclass, the foam spray model, either in steel or Kevlar bodies) in some or all of their premises including: MITIE, Kier, Legal&General, CofE, Catholic Church of UK, ShopDirect, Integral, Phillips 66, Mid Sussex District Council, Courtney Buses, Guys & St Thomas NHS, Bournemouth University, Bowmer & Kirkland, Harrow College, Saga, Empire Cinemas, Anglian Water, University of Brighton to name but a few and do not have CO2 extinguishers on site. Other sites such as some of the University of Sussex, Syngenta, Mattersey Hall and several historic halls have done similar, but with water spray or water mist
Four Fire & Rescue Services via their trading arms are selling P50 triclass extinguishers as replacements for needing both water/foam & CO2 in commercial premises.
Faraday Laboratories and the old Joint Fire Research Organisation (a Joint Government & Insurance Scientific Body) have carried out tests showing the safety of water based sprays, particularly under 1000V, at the normal safe user distance. British Rail in the late 1980's replaced Halon (used for electrical equipment fires) and Water extinguishers with Foam Spray extinguishers due to their safety in use.
The trade seem to not like anything that limits quantities hence why high performance high rated wet extinguishers aren't as commonly installed as in Europe and why electrically safe units are not sold as such and let's leave the P50 as a separate issue....