Does anyone have any idea what era this one is from?

I'd say the mid to late 70's.

Using the same criteria I posted earlier, that estimate ^ is likely off by as much as a decade. A ballpark guess would be circa 1970.

Would an arc fault detector outlet such as this add a degree of safety margin, if one is using an older electric blanket?

http://www.amazon.com/dp/B00AWJ8AV0/...ing=UTF8&psc=1

not affiliated,
jr

There was a tube specifically made for electric blanket controllers, the GL-1367 fused thyratron made by GE. It was later EIA registered as the type 5662.

It had 2 cathode pins, with a fusible link connecting them. If the current through the link exceeded 2.25 A, it would open, cutting off the power.

[QUOTE=jr_tech;3152369]Would an arc fault detector outlet such as this add a degree of safety margin, if one is using an older electric blanket?

http://www.amazon.com/dp/B00AWJ8AV0/...ing=UTF8&psc=1

not affiliated,
AFCI breakers are required, per the NEC, for circuits that feed the bedrooms and a few of the other areas in the home.
It seems that they respond to arcs and poor connections, where heavy current is consumed. I'm not sure if they would respond to a fault in a lower power item, like an electric blanket. Having never owning one and not knowing what wattage they're rated at, is hard to say whether it would respond to a fault.