I have one and used it for my toddler (at the time) and then my massive 3month old after the moby couldn't hold him anymore (it got too stretchy)
Its warm, but I think you have to be mindful of the fabric you pick. We have some pretty thick fabric selections for the panels (we got the reversable one) and it can get warm. Not overly warm/hot, but warm. Its a great spring/fall carrier for us now in WI and we need something more breathable for our humid/hot summers.
I found it to be comfy, but somewhat tricky to adjust (like getting the child snug in the back carry) compared to an ergo or beco.
And you who seek to know Me, know that the seeking and yearning will avail you not, unless you know the Mystery: for if that which you seek, you find not within yourself, you will never find it without.
I used it from the time DD1 was newborn until she was past 2 and I got pregnant again. I loved it and found it really easy to use, although I was a bit confused about the back pack carry because in order to get it to feel comfortable I had to criss cross the straps across my chest, which was doable with my small breasts but it may look awkward if you are larger busted.
I would be interested to hear how other mom's used it for a back pack carry.
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I haven't used it yet for this LO, but that's because she actually sleeps without needing to be on me :
The one I have I think would be a little warm outside in the heat, but I wear a headcover and full length overgarment so I tend to be more warm anyway
As for size, I just bought a regular and folded up the bottom for when the babes were little and then used it as normal when they were toddlers..
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