I was at the sporting goods store today, and noticed they had Fire Lites, so I figured I would grab one and compare it with a Spark Lite.
The Fire Lite cost me $10, the Spark Lite I took out of one of my spare DR Pocket Survival Packs (though they typically go for around $8). Both were brand new, unused.
First thing I did was try striking each of them. While I don't have any way to truly measure their performance difference, visibly it didn't seem like one put out a better spark than the other. Then I put them next to each other:

The Fire Lite is a tiny bit larger in every dimension, but it also has rubber applied to each side, which I found made it a little easier to hold onto.
Next, I grabbed my trusty leatherman and broke each of them apart (there goes $20

):
The Spark Lite has one long ferro-rod, while the Fire Lite has three smaller ferro-rods. When I put them side by side, I noticed that the Fire-Lite's combined ferro-rods were a little longer than the spark-likes single rod. While that means it technically has the potential for more fires, I really doubt it's a huge difference. They're close enough that it's really splitting hairs.
Which would I buy? Well the Spark Lite costs around $8 and you typically get 8 little tinders with it. The Fire Lite costs around $10, and you only get 4 little tinders with it. Therefore, I feel the Spark-Lite is likely the better deal. Otherwise, I didn't notice anything about either that makes me feel one is significantly superior to the other. In fact, I replaced my Spark-Lite with another Fire-Lite that I bought with this one, just because it was available.