Could i use iPhone 7 Kuner Case on my iPhone 6/6s for storage expansion？

Actually, we do not suggest you do this. The problem is the kuner iPhone 7 storage case does not match your iPhone 6/6s owing to their different bottom and camera design, it will affect the 3.5mm audio jack and camera if you use iPhone 7 kuner case on your iPhone 6/6s. And for the storage expansion function, it is available if you use iPhone 7 Kuner Case on your iPhone 6/6s.