I have a new blog and had many revisions due to learning my way through all the features, plugins etc, so after a month or so had 1,400 revisions in all.
This took them all out in a trice.
One word of caution. After deleting the revisions, I couldn't access PHPmyAdmin, and got a 'Cannot start session without errors' warning.
Clearing the browser cache and restarting the browser fixed that (it's a cookie session issue); a moment of panic though. It's not the plugin though, so be aware of that one.
Not tried the optimise function yet, as I don't need to, hence 4 stars.