Re: ushiro shikko?
Correct is a hard thing to get at. The easy answer is: in the first dojo, their method is correct, in the second dojo their method is. You should ask lots of questions to each, and see what it is that they are trying to teach with their method.
Aikido is a system, it points to a series of valuable lessons. These lessons can be understood and interpreted many different ways. The real goal for you is to get at the heart of what Aikido is pointing at, then you can practice and share your interpretations.