Essences can be confusing because there are first treatment essences (FTEs, like super thin toners usually with ferments) and regular essences (thicker like serums). Usually you can do a little sleuthing of the product ingredient list and online reviews to figure out what is what. You can definitely use an FTE as part of the 7 skin method (1-3 layers), but I would recommend picking up some other toner(s) to use in conjunction with that as well. An essence essence would go after your toner layers.
So AB toners are usually balancing or moisturising, and used right after cleansing. It's a very nice step but not everyone needs it. Essences and serums are usually thicker and achieve a specific purpose - such as niacinamide for brightening. You could also do without if you choose to.
Don't start new products all at once, in case you have a reaction and can't determine which product you're sensitive to