I have owned and have been using Provaris for about 3 years now and can say that it is still the most worthwhile mod to own.
Coincidentally, I own a K100 as well and can say it's an absolute steal for the price they expect for it.
If you want to get into RBAs, there's a bit of a trade off when it comes to a Mech vs a VV device. The most important part is the amperage limit the VV has, which is why people started to put RBAs on mechanical mods, to bypass that limit.
If you plan on making a single coil on your RBA, then putting it on your Provari will be fine (I'm running a built coil at 1.5 ohms at 4.7 volts right now, hits great.).
If you're looking for dual coil set ups, or super sub Ohm set ups, then you will be happier with a mechanical. There are a bunch of things you should keep in mind when using a mech and sub ohm set ups, however. This is where the safety issues come into play (battery choices, discharge rates, shorts, etc).
I currently have an IGO-W set up with very low ohm dual coils on my K100 and it hits wonderfully.
You should weigh out your options, but my opinion is that everybody should own a Provari

. Even with all the mods that have sprouted over the last year, there's still nothing like it on the market.