I am sure that, with a determined designer at the helm, that is just might be possible to make one of these things work in a perfectly safe manner, but....
I think we are running up against our cultural bias as to just how things ought to be done. Wires looping through the shower stall are not included in our list of "good things to see." That these shower heads come from places we generally consider to be somewhat behind us (in technology) does not help us to accept them.
Now, this "bias" is not always a bad thing. In the course of learning the trade, we are taught "this is the way things are done." Time and again, the things we're taught have no actual code requirement. Yet, again, we see these practices either survive code cycles unaffected, or actually see how these 'trade practices' prevent problems, and ease service, down the road.
Long ago, in another thread ("Bathroom Electric") I posted a pic of a typical Israeli bathroom....including the full-size water heater hung on the wall INSIDE the shower stall. This practice somehow seems to work for them- but I still wouldn't want it in my bathroom!
Yet, even that 30 gallon, 240 volt, 50 amp Israeli water heater could not handle a long shower, and needed about 20 minutes to heat up a tank of cold water. (The Israeli heaters are not left on, but have a switch outside the bathroom). Therfore, I rally have trouble believing that tiny shower head can really accomplish much heating- and I don't care how 'water saving' the shower head may be!
