If you get E-mails from Mike Holt, you've already read his link to the April 1968 article about the then-new GFCI's. It's an interesting read.
Let's put things in perspective.
At the time, UL still had not developed a standard for them, so listing was problematic. They were not code required anywhere - indeed, would spend the next two decades earning acceptance.
Along the way, there were many, many re-designs. Everything was changed: better 'human engineering" to reduce miswiring, as well as better internal design to reduce nuisance tripping.
The article makes note of a portable GFCI, for use perhaps with a single extension cord, that weighed 8 pounds and cost $174.50. (I hate to think what that would be in today's money .... maybe over $1000?)
As a side note, I remember the controversy surrounding this device when it first appeared. There was considerable opposition .... up to that point, the preferred way to address shock hazards was with current limited, low voltage electrical systems.
If you ever enter a kitchen, flip a switch, and hear a 'thunk' from somewhere in the ceiling above, chances are you have found one of these lighting systems; they used relays to operate the circuits.
There was also a movement to 'go European" and limit bathroom power to a power-limited receptacle for your electric razor. (The 1800 giga-watt hair dryer had not yet reached the market.)
Another interesting note to the article is that many of the electrocutions described can only be attributed to exceedingly STUPID practices by the casualties. My favorite is the guy who sat in the lake, on an inner tube, while drilling a hole in his boat.
