I got one a while back for my older 1st generation Chromecast units and it worked good for them (though it didn't solve the technical problem I was having with my chromecasts).

However on the 2nd generation Chromecast units, I don't see an indication showing that they're even making use of the ethernet portion of the peripheral. For the 1st Gens I could have sworn there was an on screen indicator showing the ethernet icon. Whereas for Gen 2's nothing, just the indication that they are connected to the Wifi network. That let me to conclude that these ethernet adapters were only compatible with Gen 1, and for Gen 2 they were just a fancy power supply. Not sure if that was true. But since it didn't solve my problem then I suddenly stopped caring so I didn't research it further.