We have been using it for a year - it is pretty good. It's not htat expensive, maybe $50 / month (I don't remember, but its not enough for me to worry about it).

It actually provides useful scans of your server and when an issue crops up I send the results of the scan to my hosting provider and they fix the issue.

I didn't do a good test of how it impacted sales but it seems to have decreased the number of calls we get asking "is your site secure".