Hmm, the cost aside, there are a couple of other functionality issues with this -- at least in OS 10.6.8.
Upon opening, a little preference window opens, which allows one to modify things; however this is the only way to communicate with the program; although an icon appears in the right menu bar, clicking it does nothing. Nor does the application show up in the dock. The only way I found to quit it is to open Activity Monitor and kill the process there; it does not show up as an application in the force quit menu.
The developer's site does provide a documentation page; however, it is not terribly illuminating. For instance, it says you can add sounds to different keys, but it doesn't say what format such sound files need to be in.
But hey, the typewriting key sounds are good and sync well with keystrokes, i.e. there's no delay, so it puts out as promised in this respect, and that is what primarily matters.