Hi
I don't have twins , but I do have two in diapers(moving into pull-ups Yah!). When my baby was born I got the SKIP HOP DUO I had the single before it. All I can say is that it has been great. It does seem big at times, and it is more wide and narrow. I have found that it fits better onto a double stroller that is a side-by-side style.
I would buy it again if I was in search of a diaper bag to hold things for two. It also has great pouches inside to keep things organized.
HTH
Mandy