My goals for authoring Klein was to provide a library for performing all manner of geometric operations using the language of Geometric Algebra. The benefits are that the formulism is exception-free (meaning, for example, parallel planes have a well-defined line of intersection, that projections to higher/lower grade entities make sense, etc), and works equally well on points, lines, and planes. Practitioners coming from robotics/animation will also find the entirety of the Lie algebra/group inside GA as well for smooth interpolation, etc.
As a graphics engineer, I found most libraries out there unsuitable because of performance reasons. We're used to having nicely packed SIMD optimized quaternions for example. Klein fills this gap and (hopefully) in a manner where you can use it even if you don't understand the Geometric Algebra (yet!). Over time, I'd like to round out the documentation to explain the underlying theory, which I find unreasonably elegant and has shifted my thinking in the last few years.
Let me know if you have any questions about Klein or geometric algebra!