In my opinion it is worth to invest 19$ into the UE4, because it is:
- easy to use
- blueprints
- active community (even the staff from epic games is active in the forum)
- official youtube tutorials + many tutorials from users
- starter templates
- demos
- …
There will be some pretty important updates, but not so often. When you start using the UE4, just take a look at the tutorial series from epic games