I'm currently in Level 2 of the German course, & I have a comment that could probably apply to all of the language courses. One has to ask oneself if your goal is to become FLUENT in a new language, or just to become FUNCTIONAL. Nothing revolutionary there; it's a concept frequently discussed in language teaching. Could I understand & be understood, if I were among friendly, helpful native speakers?
It appears to me that Rocket German's goal is FLUENCY, but it also seems like fluency is an unrealistic goal outside of a submersion experience in the language--something that won't happen for the majority of the course takers. FUNCTIONALITY, however, seems a more realistic goal for those taking an online language course, who may travel intermittently to a German-speaking country, or episodically need to understand written or audio content.
I realize it is a slippery slope when it comes to language teaching, & easier said than done. You don't want to teach people bad habits or incorrect language that they would have to "unlearn" if they wanted to move on to fluency. But I wonder if, in addition to the three levels in the language course, you might consider an alternative "functional" branch? The Survival Kit lessons are the closest you get to that, but…not really.