Well, basically when you install this it edits your current Minecraft, removing all mods, adding random stuff to the .minecraft folder, removes all servers, and essentially, makes it more crappy.

Before I had the current launcher, if I was on Tiny render distance, say there was 124 Chunk updates, my FPS would be 124. And the Tiny would have the same effect as Extreme render distance. I downloaded the launcher, and it messed alot up. It took a long time to fix everything and, it's still nowhere near fixed.