My BFF had one for her first baby. It got too stretched out to use with her second. It is similar to a K'tan (or the other way around, I think the Baby Nest came out first). The key is having the right size for your body. It has to be snug to get baby high enough for safety and your back's comfort (baby's head should be high enough to kiss). Because it is stretchy, it will probably max out in comfort at about 15 lbs. Personally, I prefer the truly custom fit that a wrap gives me. But, not everyone is into figuring how to wrap, so these kinds of wrap adaption carriers are appealing.
I'd agree - nice for newborns if the fit is right. It should NOT ever be used for back carries like they show on their website - it's far too stretchy to be safe and since you can't exactly tighten it, it's even more unsafe on the back than something like the moby is that you can at least tighten (but is still too stretchy to be safe on the back).
Re: Bought a Baby Nest/My Nest carrier
More Green For Less Green
Breastfeeding Counselor with Breastfeeding USA
Babywearing Guide ** Newborn Carriers
Cloth Diaper Guide
Safe Bed Sharing Info
www.becomingmamas.com