You may have some sort of a page cache or opcode/memcached cache active there. The plugin does not hook into the regular wordpress functionality – aside from checking on the search archive if it should override the search results with it’s own. It should not do that much harm though.
If you want I can try debugging it via FTP by testing/correction the code parts line-by-line to see how the performance changes on the archive pages when the plugin is activated.