I haven't changed from 8w, and other tanks have been more normal with emptying ..still, as you say, as long as it's good, it doesn't matter that much!

...apart from me running out of Honey Lemon Menthol. Got some coming though!
The Unitanks come with a single coil (plus 2 spares).
I'm keeping away from dual coils: my Glass Evod had only been used since I got the MVP, and I changed the used up coil for a single one a couple of days ago, and last night it started leaking!

I had hoped it would work OK with a single one, but Terry says he's had a number of dual coils that leaked!
I almost bought a few from FT, but you're right - may as well get them here while they're still a good price! The exchange rate is around 1.68, so not really worth it.