I tried this software and I had a terrible experience with it. While inputting text in the WYSIWYG window, it seemed to take forever for it to show up in the output window. At the time, I was using a portable version of NVU, and despite the fact that NVU randomly crashes from time to time, I found it much easier and less frustrating to use.
Also: KOMPZER is an NVU clone. I've heard rumors that the Kompozer app was unauthorized, though I cannot substantiate those statements. I know that the author of NVU hasn't updated the app since 2002, and that Kompozer does contain updates. Either way, they're the same program, and I've had the same (consistent) results.
I support the open source community... they really care about the software. Just wish I knew how to program my own stuff.