The comet and cosmos are amazing separately, but if you put enough of them in to change the feeling of the cube it will start to feel sticky. It feels as if you have to pull the lube off the pieces when you turn it. I find that comet works well for the insider parts of the cube, and the cosmos works better for the edge to corner contact.
I feel as if it's better to buy the variety pack so you can try all the lubes, these two included. I don't feel as if this bundle is worth buying. Based on how they work individually they should work well together theoretically. However, together I don't feel that they work well together.
Neither of these lubes work well in bigger cubes. They do almost nothing until it starts to feel gummy. The comet works well for 3x3s, and the cosmos works well for my squan. You might as well get a much faster lube like lunar or martian to make bigger cubes faster. Both lubes work well separately for the 2x2.
However, you are saving 8 cents by buying both of them together.