I agree with the sentiments above, it is a fantastic trick, and you allows for a wide range of performance options. The type of plastic bag is important however it is very common and can be found at any grocery store.
I definitely recommend getting it but like anything else, make sure you really practice it to get it smooth. This is one of those tricks that if done well will play really huge but if you just rush out to perform it and look clumsy then it's a total waste.