I have been using this for a few years with no issues on many sites.
I have run it twice in the last two days to try and get it to make a sitemap for my site using the live website so it spidered all dynamic links
It ran for 4 hours and spidered 21000 pages perfectly. It then opened the Edit the Sitemap box at the end - but NO PAGES WERE IN THE LIST
However on both occassions it failed to write the XML sitemap leaving a 1K file in place of my old one with just
<?xml version="1.0" encoding="UTF-8"?>