Since we're basically answering with our opinions, and not to step on any toes, but here's mine.
Keep in mind that you get what you pay for, essentially. While that statement isn't always true, and YMMV, but it's a good rule of thumb. If you buy a 20 dollar VV
device, you're getting a 20 dollar device. I have a couple...they work, more or less. I doubt that their electronics are very accurate though. Most of them at the low price range are made of very low quality material. I had a VV Gripper when they came out. Again, it works...but I always felt like I was going to crush the thing.
When you work your way up the ladder, you'll have to find the point where you are comfortable with the quality and the price. I have a Silver Bullet with a kick and kick extension sleeve. The Bullet + Kick + Sleeve cost more than my ProVari. Considering that my kick bit the bullet (no pun intended) after about a year, and I had to replace it (the kick). I'd say it was a good investment, even if the kick was a bit touchy.
I've only had the ProVari for a few months now, so I can't say about the reliability of it in the long term, but compared to the kick/Bullet, the 18490 battery lasts about the same time in the ProVari as an 18650 did in my bullet. More than likely that was because of the limitations of the kick itself though.
A couple of my friends have the Vamo, and they're happy with them. I'm sorry that I can't provide anything further than a philosophical response to this, but hopefully it will help in your decision.