The 4" cold cathode, simply put, is awesome. It's small size allows for a multitude of uses, especially if you'd like to light up a mini casing you've modded, maybe one of those small form factor PCs from Shuttle, or a custom mini-acrylic case.
The quality of Sunbeam's kits shows, as the build is very sturdy and the light being a nice bright blue. The inverters are very well built too, allowing one to mix and match cold cathodes, or simply to connect two cathodes of the same color.
The heat output from the cathodes themselves were minimal, as they were only slightly warm to the touch. The only other significantly warmer component was of course the inverter, though I doubt it's heat output can affect the overall case cooling scheme in any way.