That's almost certainly the pressure relief device operating, so it's not a failure - it's doing what it's supposed to do.Both electric showers I have owned previously failed disastrously with water flowing out of the shower body/control unit. That's a 100% failure rate. I got out of there fast, I can tell you.
The PRD is easily and cheaply replaced, and from what you said it was probably triggered by the flow being restricted by limescale buildup in the shower head. If you live in a hard water area then regular maintenance of a shower is essential, and if it's not done you shouldn't be surprised if things go wrong.
And anyway - I still don't see how water coming out like that is going to harm you.
So on the basis of two old and poorly maintained showers from the same manufacturer you condemn the whole concept of electric showers as "bad news"? That's bit like condemning cars on the basis of having owned two old and poorly maintained Morris Marinas.The first was a Triton T30, the second a Triton T60. Both were old.
Fair enough - they aren't the best solution for everyone - I was just questioning an opinion which seemed to be insufficiently logical and partly based on superstition.Maybe a brand new professionally installed electric shower would work OK for a few years? I doubt I'll ever be in a position to find out.