I saw some. I think it's a very interesting concept and design.Chacos look like Birkenstocks to me. Never tried either kind. My favorite shoes of all time are Z Coils. They have a spring at the heel that really helps to support you. They are FAR more steady and solid to walk on than they look. They are NOT cheap, but if you get them at a good store, one that specializes in footwear for people with medical problems, they can adjust the springs to support you. The springs can be adjusted so if your foot rolls out (or in) or you have other problems, they can really help. I got my first pair at a thrift store, where they told me that they looked like really good shoes so they had to charge me a whole $5 for the pair. I had another pair after that one and I am planning to buy another pair in the next few months.
At one point I had been wearing the first pair and I stopped in a store that carried them. I didn't know they could be adjusted, so I let them do it. They were already the most comfortable pair of shoes I had ever owned, and the adjustment made the biggest difference.
I know these are outrageously expensive, but they are worth it if you are on your feet a lot. I have arthritis in my knees and hips, and chronic back problems, and these shoes made a HUGE difference.