This past Christmas, my wife decided to spoil me with a keg setup from Midwest Supplies. It's exactly what I wanted to carbonate my water and stop dealing with club soda or dry ice (which seems to be strangely lacking in any of the supermarkets where I live).
It's extremely easy to use, though a bit more difficult to clean. I'm not so worried about the cleaning part unless I'm actually carbonating a beverage in it instead of just water.
There are some other pros and cons worth mentioning.
Ease of use.
Volume - It's very handy to have 5 gallons of carbonated water to bottle some beverages with, much better than that silly SodaStream contraption being peddled lately. 20 times more volume for 1.5 times the cost. I'd say that's value. I'm not sure how many gallons I'll get out of a 5lb CO2 tank, so far I've done 3 and still holding strong.
It does take some time to carbonate, though I'd imagine not nearly as long as would natural carbonation from yeast. Overnight seems to do the trick just fine, but I've also read a day for every 10psi.
If you do actually put a beverage in it other than water, you get lots of foam coming out (which is very bad for bottling, and difficult to serve in cups), and you're o-rings tend to soak up the flavor. You can switch sets, but each additional set is around $10.
Don't let the kids knock over the CO2 tank and damage the regulator, that could be dangerous.
Difficult to chill 5 gallons of water.
So over the month that I've played with it, it's been a lot of fun, but still not quite getting the carbonation in my bottles that I'm looking for. I've been close and I'll share my progress and recipes as I can. For all the cons, the pros definitely win out. Now I just need to get more ingredients.
Which is where the next little bit comes in: Monin syrups! They have an excellent array of flavors and you can order directly off their website. My wife picked up the Green Apple, and at the right concentration, it tastes just like Jones Soda's Green Apple. Though unfortunately not any more economical. One bottle of Monin will make a little over a gallon of soda at that concentration, which is about 11 bottles. You can easily get the same amount of Jones for the same price.