I have two of the 91/4500 dye throttle air systems and i love them. They are extremely light weight, lighter than other systems ive used, and in my opinion much more durable. In my opinion the performance is also better than the others ive used. The retail on these tanks are 240-280 which is outrageously expensive, but on ebay and some websites you can find em as low as 140. I got both of mine off ebay for $300 shipped with two tank covers.
Definitely look around for a good deal on one, it is worth it. It deserves a 10 in the air system category because it is the best.