I am asking this question without having used this application because the output in the screenshoot looks familiar. Is this simply a frontend for the unix command fs_usage?
If it is, $20 is a pretty ballsy ripoff for a simple gui to someone elses application. If it isn't, what can it do that fs_usage can't?

For the curious, your Mac comes with fs_usage. To try it out, here is a sample command:
sudo fs_usage -e -f filesys|grep -v CACHE_HIT|grep -v grep|grep -v mds

The -e prevents fs_usage from monitoring itself, the -f filesys make it monitor only filesystem activity (as opposed to network activity), the various grep -v foo parts tell fs_usage to ignore those various things (i.e. grep, mds, whatever else you don't want to monitor).

Why would you want to use it? If you have an app, say Safari, that is giving you the spinning pinwheel of death, fs_usage would be able to tell you what was going on when that lockup was happening. Might point to something you can fix (like a cache file that should be deleted). Of course, fs_usage has to already be running when this happens.