I really didn't like the Baby Bjorn when I used it with DD1. I felt like I was using it incorrectly as her position always seemed uncomfortable to me, but I've heard a lot of people say that the Baby Bjorns aren't designed to hold babies in the right spot, and it can be bad for their hips. I didn't know that until recently but FWIW I stopped using the Baby Bjorn because it was uncomfortable and time-consuming to get in and out of. A lot of people have recommended the Ergo carrier to me, I haven't bought one yet as DD2 and I are more than happy with our Bubba Moe sling, but I definitely have it in mind for the future. I've read that Ergos are better-designed and hold bub in the right position, giving their hips and bottom the support they need.
HTH, good luck