What would concern me most about that system is(road salt) water ingress in UK riding conditions,the whole kit and caboodle is right in the firing line unless some wide mud guards were fitted with very effective mud flap.
The ladywife's Fazua-equiped Focus Parlane2 came with mudguards fitted as a standard part of the bike. They're very effective, although the BB and battery/motor-capsule do still get splashed with water and mud a bit. It doesn't seem to bother the interface between the motor and the gear box, which is a tri-cog affair running in sealed bearings on both the gearbox and the motor shafts.
The handbook does suggest regular and thorough cleaning of this interface post-ride if conditions have been wet & dirty. On doing so, the interface looks well-protected and doesn't seem to suffer undue water or muck penetration. The bikes are advertised as suitable for gravel and other mucky-wet courses as well as tarmac roads.
I would be wary of riding on highly-salted roads. But then that's true for any bike, electric or otherwise. I've seen what happens to a salted wet bike if left for any significant time post-ride without a thorough wash, clean and lubricate! But I suspect the Fazua systems are rather better sealed than a lot of ordinary BBs.