Yeah, I think those are neat, Gareth!
I much prefer "hard gels" (plastic filters) for correcting strobes. I really don't like using adhesive tape, or adhesive-backed Velcro to attach gels and diffusers to my SB800. The tungsten correction filter ("hard gel") is often most useful. I wish I had a set of these for my SB800, but I never seem to get around to finding/ordering them. As a result, my SB800 has sticky tape residue and thin strips of Velcro all over the damned thing.
I have a pile of older, manual VariPower Vivitar 283s, each with a set of Vivitar hard gels which "snap" neatly and securely into its Vivitar plastic gel holder (too bad Vivitar discontinued this particular "version" of the cheap and powerful 283). The Vivitar holders were really cool--they're designed like mini softboxes, and are slightly larger than the flash head, increasing the size of your source slightly. I think the convenience and durability of these kinds of filters is well worth their rather insignificant expense.
If you want the finer correction available from a (free) Rosco or Lee filter swatch, you can always pull the holder and tape that on instead (or, tape it permanently to a clear hard gel, or a custom-cut piece of thin polycarbonate).
