I'd much rather have the metal Spark-Lite which has a replacement flint and can be used forever. The Spark-Lites are a great design with ease of use in mind. However, the plastic ones with the one flint inside tend to oxidize away after being used the first time. The speed that it deteriorates depends on where it is stored/carried and environmental conditions. This makes depending on the plastic Spark-Lite somewhat risky.
Interesting, I didn't know that. I have several and have used them for at least a year with no problems, but then I keep them in a zip-lock-type bag when they're not in use. I've been ogling the aluminum version for awhile, so maybe this will be the excuse I need to get one.
I will say the brass one from TAD is really good, bomb-proof and well made. But even so I find the square shape of the Spark-Lite to be easier to use.