I just ordered and received 6 of the new Thirsties Duo All In Ones; 3 in each size. My first impression was LOVE these as I eagerly pulled them out of the box, all the while thinking that I hope that they will fit and perform as well as they look. So, after prepping and trying them out, here are my thoughts.... Oh the potential they have to be PERFECT! Here are the general pros: adorable, two adjustable sizes, trim, buttery soft stay dry fleece on the inside, can easily be turned inside out for faster drying time, easy to add a doubler to the tunnel, available in snap or aplix closure, (I chose snap) gentle elastic, easy to spray off EBF or solid stool. Now the cons for each size, and really the cons are about the size/ fit, nothing else. Size one: there is less snaps on the width than the Duo Wrap making not enough size options at the waist. My little 10 lb. 14 week old is on the middle rise and the loosest waist setting on the AIO, but on the Wrap he is on the middle rise and waist setting. So the only problem is it needs more snaps at the waist, other than that it is perfect and I love the fit! The size two has the same problem, but also needs a bit more rise and width in the booty area IMO. There is NO WAY this would fit to 40 lbs! My 2 1/2 year old is 26 1/2 lbs (he is average build and fairly slender 15th percentile) and is on the loosest settings. It looks a bit small, but is still comfortable as long as he doesn't grow! It is most definitely smaller in every way than the Duo Wrap, so be prepared for that. All in all it is still a fantastic diaper!!