I mix their 4 oz tobacco doubler with higher nic juice and go through 5 mls a day. I can work through those pretty quickly. I'm doing 6 mg too.
If you're a single-flavor vaper, it can make sense. I like having 4 or 5 flavors around at any given time. The least amount you have to buy is a 2oz doubler and 2 1oz bottles of 12mg. Or buy just the doubler and a high strength unflavored. Been there, done that, just tossed about 6 ounces left from 2010. I'll do it for their Caramel Popcorn, but not for anything else. (I haven't even tried some of their newer flavors like cupcake because I don't want to make that commitment.)
Right now I'm concentrating on Deejstuff. His most famous flavors are champagne (it tastes like champagne -- which I hate), cheesecake (just ordered my first bottle but I'm not a big cheesecake eater) and fruit flavors (I prefer candy.) So far a few of his flavors are on my "rotate them through the collection" list but I haven't found the one or two for my "must be in the apartment at all times" collection core. But I like them enough to try some more. (Now that I've dumped my antique TV waffle, some of those are will be tasted soon.)
And my third liquid vendor is Kick Bass Vapor. Their Gooey Better Cake is must have. I'd drink it if I could.