Came here expecting to see this as a top-level comment. Really not sure why someone (here on HN) would pay $30 rather than just write a simple script like this.
I could see paying $30 for the options/playback. I'm not sure if `screencapture` gets all the desktops or just the active one or what. Also the playback UI looks nice and is a much better way to check what you were doing and for how long than a directory of images would be. If it was a subscription services I'd be looking for alternatives but one-time purchase? $30 seems reasonable.
Based on the man page it captures the 'screen' for all monitors unless otherwise constrained by options.