pure lemon oil is probably also essential, but like any marketing claim, you just need to check.
If you've read the other threads, then you understand that you don't want something like lemon flavored mineral oil. You want an oil that is produced solely by squeezing the zest (yellow colored portion) of the rind.
Check the ingredient list, or whatever it says about how it's made. As long as it's just lemons, you've got the right stuff.
I happen to be using Boyajian, and they leave out the word essential. It basically just means it's the essence, and it sounds cool for marketing purposes, but it's still just pure oil from lemon zest.