I tested my first Kozy sometime in 2003 (the date is a guess) or possibly early 2004. It was something of a revelation for me, the whole concept of mei tais, and one of the first children I wore in it weighed 55 pounds and was 6 years old...and we were both comfortable. I'd been wearing babies and trying new slings and carriers since 1993, and ten years in, this completely changed everything I knew about babywearing.
My first tester, I reluctantly loaned to my cousin in the spring of 2004, reluctantly because I knew we would be trying to get pregnant soon, and I desperately wanted to have it for my own daughter.
I never got that carrier back. My cousin loved it so much, and her son got so attached to it, that she bought me a new carrier, and Kelley sent me a silk as a gift before my second daughter was born in 2005. My black velvet and blue brocade silk Kozy was one of the first carriers my daughter was carried in, at 2 days old, when we went to a midwifery conference, and it will be one of the first carriers I wear my son in this winter, when he is born in late December. Kozies can run the gamut from casual to drop dead gorgeous, and I've never met one that wasn't comfortable.
Now, once my daughter developed opinions, she liked having her legs out, and had very, very short little legs, and we used other things for a while with a narrower seat base, but I know in a pinch, even with her at 43 pounds and six years old, I can always go back to my Kozy if I am allowed to carry her at all.
I've had at least 150 carriers go through my hands, and I loan/gift many, many carriers. I've loaned my canvas Kozy once or twice but always gotten it back. The silk? That one may get handed down to my kids. They are that durable, and that comfortable. Though I may keep it, for wearing my grandbabies one day. I've had other carriers I liked better for one stage or another, but even with all the innovations and designs that people have come up with since 2003 for other brands, Kozy hasn't changed a lot, because it didn't have to.
I never worry about construction or worksmanship on these... they're capable of supporting the full weight of an adult (and though it looks silly, I've seen more than one adult worn in one of these.)