I see all the horrified responses from Australians... Have you forgotten the type of electric kettle you used to have before the modern sealed element type?
Flick through the photos on this auction...
http://www.graysonline.com/lot/0034-3127463/artworks-and-antiques/retro-electric-kettle-by-npa-with-bakelite-lid-australia-c-1950
Some of them didn't have a resistor element, just a couple of closely-spaced plates. They depended on the conductivity of the water.
The auction says 50s vintage, but the type was still common in the 80s.
I've been around a very long time & I've never seen the "couple of close spaced plates" type.
The other type was ,indeed,common.
Several points:-
(1) As long as the lid was down,you had no access to the water or the element-----none of the ones I saw (hundreds) would allow insertion of the power plug into the kettle body without the lid being closed.
(Of course,if the lid is broken,or removed,all bets are off,as you could then touch the connections to the element.)
(2) Australian power points (GPOs) are all switched,so it was normal practice to turn them off as soon as the kettle boiled.
(3) You
could pull the plug out of the jug while it was still switched "ON",and possibly "zap" yourself,if you weren't careful.
(The kettle plugs were a lot crappier than IEC ones,& having them come apart in your hand was a more likely shock cause than via the hot water.)
Compared to the so-called "cordless" ones common today,which present Mains voltages at the "base" unit,and rely on a bit of flimsy bent metal to disconnect Active if the kettle is removed (if the factory in the PRC didn't get it wrong),these old beasts come out quite well.
Back in the late 1950s,the normal type of Instantaneous Electric HWS was either a 3 phase box mounted in the roof,or a single phase one on the wall (in the bathroom) with Earthed metal piping to the shower head,
Around that time,there was a big sales push in West Oz to sell similar devices to that in the OP's posting,except they were all metal.
They just seemed to disappear off the market----whether the State Electricity Commission "lowered the boom" or they just weren't popular,I don't know.