Invisible Prisma has great knot strength, and it's easy to tie, thanks to a special coating and slightly greater stretch. It is still a hard material so it gives you great turning ability if you use heavily weighted flies and due to the density of the fluorocarbon it sinks, making it ideal for wet flies in really clear waters.
The fluorocarbon line is wound on a classic barrel spool which allows you to attach several spools of different thicknesses together instead of having loose spools lying around in different pockets.