I just read all the chapters available and... i really don't see what people are whining about. This is kinky as hell? Hell Yeah. This is ntr? No.
The two couples clearly like and i could say love each other, this series isn't about betrayal... it is about exploring desire, they have things they want to experiment.
Sure Miko was forceful in the beginning but in the end, i can say with confidence that she did that only because she knows her partner wouldn't mind, if she felt different she would have talked to him and she clearly wants to everyone involved to have fun and be happy, she doesn't want only her desires being satisfied.
Now if you don't like the manga because of the story or the art it is fine, it is your opinion and no one has the right to disrespect that but don't mistake this as ntr, this really isn't.