Nice avatar rcflow.
When I decided to buy rather than build, I thought about how I was gonna use my new toy. I'm a herb user, mostly, rather than essential oil, and I use my T1 or Evo core for that. But I've found that my stealth needs revolve around the smell part, rather than the visual part, and for that need I've switched over to PG and my DART. Small is still important, as well as speed of use, but the smell factor far outweighs everything else for
my stealth needs.
I'm pretty sure I'm going to buy (or build) something based on the new Evolv DNA 20D 20 watt control board, for use with my existing T1 or (more likely) Evo core, and retire my T1 battery holder, the same as I've retired my Ultra battery holder. With a suitable adapter, the Evolv 20 watt supply should also work for the new Cera cores. But I also realized that I had a bunch of 14500 batteries (for my Ultra), and that a regulated voltage (or wattage) base would be MUCH better for my DART cores, and that I didn't want to wait until I got around to building something. Plus 20 watts is way more than a DART core needs. (I run 10 watts into mine, and it's plenty; I could get by with 7 or 8 watts, but I like the fast response and dense hits I get with 4.0 volts, which is 10 watts into my 1.5Ω DART core).
The SmokBox VariCool 6A Beast costs about twice as much as it would cost me to build something using the same parts. But I had it in a few (3) days rather than the couple of weeks it would probably take me to order and receive and build something. That was worth the $30 extra to me, particularly since I plan on getting/building a more powerful device in the future. I have been EXTREMELY happy with the SmokBox VariCool. Extremely. It is SO much a better experience than using the unregulated Ultra battery holder. The single only thing that bothers me is the looseness of the battery cover. This does not effect usage at all, nor do I think it will break, it just feels cheap.
I again want to mention that the quality of the case itself, as well as the mounting of the 510 connector on the top, is not up to the level of the commercial metal tubes that compete with it in the same price range. On the other hand, none of them use the same switching regulator used in the VariCool, and none of them provide me the flexibility of its simple circuitry (for example, they all have 10-15 second timeouts, which is NOT suitable for using the DART with essential oils). The battery cover has a noticeable amount of play, and I worry that an extremely extended session (with multiple users, not just me) will allow the 10 watt DART core to get hot enough to losen the 510 connector, which is press fit into the plastic case (and hot glued on the interior). This has NOT happened so far, and I've left the DART on for long enough that simply touching the metal DART tube is enough to instantly burn you, so it may be a fear that's not real.
As to whether you want to buy or build, I don't know exactly how to advise you. The switching regulator used in the VariCool is the exact same chip I would buy if I were building, and the internal construction is probably as good as I would build myself (assuming the same size box). The main switch used when you vape (the pushbutton switch, not the sliding safety switch) is just fine, and feels great. I've been doing a LOT of reading on the e-cig forums, and I think I've found a custom handmade wooden cased box mod that uses the new Evolv 20 watt controller (which also has a GREAT OLED display that shows you voltage, core resistance, and wattage simultaneously), but also costs twice as much ($130-$150) as the VariCool box we're talking about. It also uses an 18650 battery (or two 18650s, or two 18490 batteries, or even 26500s. You can get whatever you really want; it's custom made), and hence is much larger (though it's still pretty small) than the VariCool box, which uses two 14500 batteries. I'm pretty sure that's what I'm going to wind up buying in the near future. I love wood, and the quality of his woodworking on the mod is second to none.
I would hazard a guess that if you love building stuff, you're at home with a soldering iron, you've found a suitable box case that you really like, and you're in no particular rush, then building one is probably a good choice, and will save you a little money. If you don't want to bother, or don't feel particularly qualified to design and build something, or even if you're just in a rush, then you could do much worse than buying a VariCool.