Well unlike the previous reviewer, I actually downloaded and tried the plugin before commenting.
Here is what I found:
1) The plugin DOES work with Photoshop v4.
2) The download is packaged as a OS X DMG file - rendering it very difficult for Mac OS 9 users to do much with.
3) The "documentation" is a single RTF file that can't be read on a Mac running OS 9.
4) There is no information provided informing me how to pay for the product and obtain a license key.
5) There were no samples provided showing me what to expect from the plugin.
Since the author is targeting Photoshop versions that were part of the Classic Mac OS era, it seems odd that s/he would create such a product and then package it for OS X exclusively.
And since I was unable to determine what the plugin actually did (other than leave a watermark on the image I used for my test), I can't give any stars to the product.