Great question! But there's absolutely no catch, for real!
The reason we're giving this away for free is that it leads nicely onto a new course we're offering which takes you on the full journey to complete mastery of foundational Java. That course is a paid course which we hope you'll enrol in - but there's no pressure to do so. And if you don't, no hard feelings and we're just pleased you got some value out of it and we're happy that we set you off on the road to discover the exciting world of Java and the great career it brings!