I've always thought of stuff like that as a backup plan only. If something were to happen to my primary controller I could run my laptop straight into my ceremony mixer and mix directly on the laptop. It wouldn't be fun, but I can do it.
It's a fun way to goof around...but certainly not worth $29, IMO. For FREE, yeah, I pulled it down (I'm not even a Serato user...but FREE stuff when I have some time on my hands...).
The other DJ software I have used INCLUDE the keyboard hotkeys in the base package...and I have played around with it. A single mouse click is OK, but not enough. Based on that experience, I can say that it takes practice to build the muscle memory to actually be able to DJ with the keyboard. Like 30-45 minutes a week to keep proficiency AFTER you actually get good. Keyboard overlays with the control mapping help, but with out practice....this is too risky for me.