I just learned that the tarbell course is about the same cost for all the books. if u want one trick, buy pure smoke. if u want definitive teaching on sleight of hand, staging, routining and basically all magic knowledge to make you a good magician, buy tarbell.
Pure Smoke is worth it if you'll put the effort into making it worth it. It's a well made device (other than a few which have had problems - E support will sort those defective units out) that accomplishes exactly what it says it will. If being able to produce smoke from the hands is something that you think you can use a lot, then it will be worth it. If you use it as a gag or in every trick you do, it probably won't be worth it as you won't be using it to its full potential.
It's neat, but I prefer Alan Rorrison's SMOKE effect here at theory11 for 1/3 the price. For me, it's the perfect package. No crazy setup, no sleeves, and it's always with me and ready at a moment's notice. It's my favorite gimmick purchase yet. Strongly recommend it.
Pure Smoke is not "a trick". It allows you to turn something as simple as a colour change in to real magic. The appearance of smoke takes tricks you already know, to a new level.
That being said, I have found Pure Smoke to be quite unreliable. My first one broke within a week. E were alright about it and sent a replacement out free of charge, but it took 3-4 weeks to get a replacement from the initial email explaining that it was faulty. It's not just me either, a lot of people have had problems with the device and for that reason I wouldn't advise anyone to buy it.
It is amazing though, when it works, but I would suggest that you wait and hope they release a revised edition. Because of the reliability you're running the risk of paying a lot of money for a device that may not last long. I'm almost scared of using my replacement, because I know that one day I will go to produce smoke and nothing will happen, just like with my original device.
So, if you want to produce smoke then buy it but don't be surprised if it breaks.