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).

The "problem" I was attempting to ask about, SportsPhotoGuy, was not "why use a gel" but rather "what is so wrong with the inexpensive gel sheets I've been using for decades that I'd want to plunk down an order of magnitude more money, and lose versatility in the process."

Bulky and single-purpose, yes...but since I already have a gel more or less permanently installed in one of my SB-600's, I like something that is more durable AND easier to change. Vive la difference! :)

The problem, of course, is the difference in color temperature between the flash and ambient lighting...try shooting someone in a typical business environment under fluorescent lighting, and you get a nicely exposed person living in a weird, greenish environment. The gels balance everything out quite nicely.

Looks a lot bulkier and single-purpose than a leaf of inexpensive gels and velcro.

What is the problem these correction systems are trying to solve?

For $1 more one can get 15 5x8" gel sheets of color:
http://www.mpex.com/browse.cfm/4,11815.html

Or 11 5x7" sheets for correction:
http://www.mpex.com/browse.cfm/4,5881.html

And that's for package bundles. If you want one color gel sheets are about as close to free as anything in photography.

Now I think the SX-3FL and TN look useful.

http://www.nikonusa.com/Nikon-Products/Product/Flash-Filters/4966/SZ-3FL-Fluorescent-Filter.html

http://www.nikonusa.com/Nikon-Products/Product/Flash-Filters/4965/SZ-3TN-Incandescent-Filter.html

any thoughts on the changeable?

http://www.nikonusa.com/Nikon-Products/Product/Flash-Filters/4974/SZ-3-Color-Filter-Holder.html

http://www.nikonusa.com/Nikon-Products/Product/Flash-Filters/4967/SJ-4-Color-Filter-Set.html

it costs 1220 + 2360 yen to buy seperately, just as well it come in the pack!