I love my babytrekker. It's super comfy and once you figure it all out, I find it rather simple to use. My sons both seemed to feel comfortable in it and I was able to use it with my second boy from birth to a bit over 18 months with no issues. I'd have used it longer but I mostly use it to take walks and started letting him walk around with us a little after that and then I got preggo again and carriers just don't work so well when you're pregnant.
Anyway, I look forward to using it with my third child. I'd certainly recommend it and really like the new feature of the stirrups. I'll have to see if those are available separately to use with the older carriers maybe. I think the stirrups are an answer to the problem of kids kicking the backs of your legs when you carry them in the back carry.
It has the ability for multiple carry positions. The 2 back carry positions are the biggest challenge at first but I figured it out pretty quickly and I really like the backpack style carry position once my boy was old enough.