I really like using vac-pots, which are also known as siphon/syphon brewers. I'll be devoting a few blog posts detailing how to use them, take care of them, and adjust them, but before doing that I think it's best that I set the table by answering the value question: Why use a vac pot when there are much, much easier ways to make coffee.
1) The result in the cup. A properly done vac-pot produces a very clean cup that nonetheless has a good amount of body/oils (assuming one uses a cloth filter). Some brew methods emphasize flavor clarity while others emphasize body. You can see where I'm going with this. I feel that the vac-pot can give you a near-perfect balance between the two, as well as a sweetness that I've never experienced in anything outside of espresso. Maybe it's the near-constant brew temperature, I don't know. Syphons can really bring out the beguiling sweetness of a bean.
2) Control, which of course relates to (1) and is important only insofar as (1) is achieved. Because vac-pot is an immersion method, you can choose dose with a flexibility that drip coffee usually forbids. A standard dose will give you something delicate and almost tea-like, whereas an up-dose can deliver a result that is perhaps less complex but has excellent intensity/focus. You can also control temperature to an unequaled extent, and indeed get something like a flat-line brew, which means consistently good coffee (once you figure out your method).
Other people may have other reasons for liking the method. It produces quite a show and can be romantic when done table-side. For me, it's all about the taste. Syphons done right are delicious.
Which leads to an important caveat: it's not easy to do right. It's not so hard to get a good cup out of one, but to get a great one, one that justifies the extra effort--this will probably require of you much trial and error. Fortunately, Roast-E sells Yama vac pots that are fairly inexpensive. If you want to experiment with vac-pot, you don't need to make a big investment.
Soon I'll follow-up with a post about how I like to use them. I promise that no esoteric Zen "be one with the grounds" stirring techniques are required.