I'm so glad you are enjoying learning Korean with Rocket Korean! :)
Romanized Korean is a relatively recent phenomenon in the history of the Korean language. Most Koreans do not use the Romanized alphabet and in fact many can't even read it. The Romanized alphabet is a phonetic translation of Korean script meaning that it is written how the language sounds. As such there is some disagreement over how vowels should sound as well as some dipthongs (two vowels together) and double consonants. Because of this the Korean government introduced an official Romanized alphabet in order to try to standardize it, however in practical everyday life, it is not something that people are using and it has also come in for strong criticism particularly in South Korea.
In light of this, and because Rocket Languages is focused on teaching everyday conversations that you are likely to have in Korea, our Korean language experts took the view that it would be better for learners to be taught a Romanized version which is tailored particularly to English speakers and the sounds of the English language so that it focuses on teaching how to pronounce the words, building confidence in speech. However, the course also provides writing lessons and full Korean script in every lesson so that you can learn to recognize written Korean as well.
I hope this helps.