Adding new features as KickstartCassiopeia does, can have an impact on performance.
During development of this module we always try to have this impact to be as minimum as possible. We do this by adding small scripts, minified, and clever programming.
Below you can see the impact the module has on performance.
First, GTMetrix without the module enabled
Second, GTMetrix with the module enabled
As you can see, there is a small impact, based on external scripts being loaded, such as Google fonts and some other. All in all still a very decent result. Getting an A grade from GTmetrix is always a good thing.