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. The SOL version or variation may last longer but for a few dollars more you can invest in the metal Spark-Lite that you can replace the flint in and it will last a lifetime.
I still prefer the Firesteel, I can see what I have, I can make a load of hot sparks and some models are pretty affordable. I coat mine with clear acrylic paint after each trip to prevent oxidation.