As with any warranty, there are rules. These require some action, but its not unreasonable. If you're not cleaning and lubing your chain then you're doing it wrong. This really isn't a downside to the product.
Furthermore he really asked if its good quality. It absolutely is, and the company stands behind the product.
My point is that a "lifetime guarantee" with stipulations like that is obviously just a marketing ploy and nothing else. If they really stood behind their products, they wouldn't have those requirements. Instead of a lifetime guarantee, they should just call it a "one time replacement" plan if you buy the whole package.
Lifetime guarantees on wear items like brake pads, sprockets or spark plugs are worthless unless they are free replacements forever and no questions asked. Even then, it's still kinda pointless sometimes. I purchased a power steering pump for my truck from the autoparts store with a lifetime warranty, and they will replace it as many times as I'd like. The problem is that they replace the seals with crappy seals and the pumps last about 6 months. Yeah, I can get a new one every time, but changing them out gets old pretty quick.
Sorry, but a lifetime warranty on something like a sprocket doesn't really mean jack unless it is no questions asked, which would be stupid of the manufacturer to do.
Along with the physical quality of the part, the quality that you are getting for your dollar must be considered. Sorry, but a $90 sprocket with no benifits (other than looks) over a cheaper steel one can't truly justify it's existence unless you are going for form over function.