When my DD was about 1mos I bought what I thought was a Beco Butterfly off a Belgian site, it turned out I had read the ad wrong and it said 'like' Beco, it seems to be identical apart from where the front piece attaches to the shoulder straps the buckles are right at the top of the front piece conveniently right where your babes mouth is so she chews on them or they rub her cheek!
I used it at first with the infant insert but quickly she was too big for that and too small to use it without but now at six months I think she fits it perfectly, had it on in the week with her at the front and she loved it! I really want to get the hang of the back carry though because it would be so handy to have two hands free and get some things done. I tried it out and it just didn't seem right. The flat piece under the babies bottom seemed not flat against by body but kind of pushing on me and making me feel like my trousers where being pulled down. I am quite tall and quite slim and my hips are quite prominent, should the waist strap be on your hips or above? It feels odd if it's on my hips but if it's above and I do the strap up tight enough with DD's weight it feels like it will cut my stomach in two. Also she seems to ride really low and her head seems to hang back onto the carrier like she's at an angle.
Hope that makes some sense! If any one has any tips for adjusting and wearing this sort of carrier in a back carry I would love to hear them I only had it on for a short time but I got so much done!