I have one and I love it. One of the main reasons I love it is that I find it super easy to put on when back carrying. I hate hip scooting DS around and onto my back. With the Kozy I just hook the top straps under his arms, hold on tightly and swing him gently around onto my back (the website explains how to do it better than that with pics). Super easy and I'm far less worried about him falling off as when I'm hip scooting him around.
We have an Ergo and a Kozy. I prefer the Kozy and DP prefers the Ergo. I wonder if he finds it easier to hip scoot DS as he is much taller than me, so more room to work with and DS fits under his arm easier.
The
Kozy website says you can wear your child for as long as you like regardless of their size or weight. I'm not sure if they have been tested, or to what extent they have been tested though.
We have the Windsor pattern. I'm super lucky - I got mine on special from Aquabub for just $135! Money very well spent.