I use the one featured on the website with a hot airgun and employ a plastic bag to cool down the vapor and trap small particles. This means you don't have to use water and the glass contraption cools the vapor down sufficiently so there is no risk of the plastic bag melting due to hot vapor.
I've used it on a daily basis for years so I have ample experience with it. Nowadays I only use it occasionally since I have a Volcano vaporizer and prefer to use that instead.
I like inhaling the vapor from the bag at leisure and dislike using the vaporizer directly with water since this means you use the hot airgun to blow the vapor in your lungs. I prefer vaporizers that allow you to breathe in the vapor actively instead of passively with a fan blowing the stuff in your lungs directly.
However, trapping the vapor in a bag, however shortly, will change the composition of the vapor. You can experience this by blowing cigarette smoke in a bag and inhaling it from the bag.
This will taste differently from smoke that is inhaled directly. So ideally, the best vaporizer would cool down the vapor directly and allow you to inhale the vapor without storing it temporarily to cool it down.
There are also people who claim plastic bags of any sort are unsuitable to store the oily vapor because of potential reactivity from the plastic with the ethereal oils.
I think it would be best to use glass to store vapor for cooling it down, but it's hard to find or construct a glass contraption that can be vacuumed to avoid diluting the vapor with plain air.
One nice feature of the temparature contol on the hot airgun is that you can set it very low to get rid of any excessive moisture in the weed as well as potential contaminations that might be released at lower temperatures. So you can pre-heat the weed for a while to get rid of any substances that will evaporate at a lower temperature than THC and then turn the heat up gradually to extract the THC.
Very efficient, you can get twice as high on half the amount of grass compared to smoking.
Doesn't pollute your lungs like smoking. Most herb consumers tend to hold down the smoke for 5 seconds or so to absorb most of the THC. This also means you absorb a lot of crap that arises from combustion.
With a vaporizer you can hold down the vapor for 10 to 20 seconds to absorb most of the THC and achieve a very high efficiency without polluting your lungs.
Note however that your lungs were not designed to absorb THC. So while a hit of THC is more comfortable on your lungs compared to thick smoke from a spliff, it's still not a very pleasant experience to absorb THC with your lungs.
So be careful and conservative in your estimates of how much vapor you can absorb and take in small hits because you tend to notice the 'loaded' feeling of your lungs once you've exhaled.
There is a kind of trade-off between the time you hold down the vapor and the time you keep the rest of the vapor in the bag allowing more THC to collect on the inside of the bag. I personally prefer to keep the vapor down for 12 seconds or so and avoid overloading the bag with too much vapor or vapor that is too heavy.
Since the vaporizer tends to accumulate only THC oil and no tar, it doesn't start to stink like a bong after a couple of sessions. This means you can use it extremely often before cleaning it and the glasswork of the vaporizer will always smell fairly pleasant in case you like the fragrance of herb.
The glasswork and the bag have a fairly large surface area which means you tend to loose quite a bit of THC that tends to collect on the surface and degrade rapidly by coming into contact with oxygen and light.
Also, cleaning the glasswork is quite a hassle (I recommend using cleaning alcohol for this purpose). Replacing the bag is easy and doesn't need to be done very often, although you might get annoyed with a sticky bag that makes it somewhat difficult to collect the vapor.
The vaporizer is kinda clumsy and awkward to use in general, because it is rather big and handling a hot airgun while stoned can be risky.
Be sure to keep the hot metal end of the airgun far away from the plastic bag and make sure you have a good place to put the hot airgun where it is safe to cool down. Watch out not to touch the hot metal nozzle of the airgun until it has cooled down!
The temperature control is not extremely accurate. This means it takes some practice to get used to judging the best temperature setting for a given amount of weed. If you use more weed, or if the weed is crumbled into finer pieces, this means that the airflow is blocked more and consequently the air that flows through can get too hot.
Also, since you need to pre-heat the airgun at a higher temperature setting, you can get confused with the temperature setting sometimes and accidentally burn the weed instead of vaporizing it.
It's a very efficient way to get high and a great investment if you spend a lot of money on herb, not to mention the health benefits compared to smoking herb.
The device is somewhat clumsy so it might be a good idea to save some extra money to buy a Volcano vaporizer which has a more accurate temperature control, doesn't allow you to burn the weed no matter what the temperature setting and is much more comfortable to use, clean and maintain. Also, the Volcano doesn't have any glasswork that will collect THC that goes to waste.