Update: Back in stock, and the $5 smart plug is now available with a whole host of Alexa devices. The Dot is the only one currently discounted though.
These switches effectively add smartphone and voice control to anything with an on/off switch, including, it must be said, Christmas string lights. I can turn my own tree on just by stating “Alexa, turn on Christmas tree” into the void.
This deal also works with the as-yet unreleased Echo Spot, which has yet to receive a discount itself at any point, obviously.