We do. We have it for our city select. Honestly, we never use it. We tried it a couple of times when the girls were still in their car seats on the Select and J despised it. He was scared of it and wouldn't hold on. But, he was only 21/22 mos.
We then bought a valco with Joey seat so anytime we went somewhere he couldnt walk thw whole time we use that. We will probably try it again now that he is older.
I will say it made it hard to push the stroller though because it sticks out. So I was awkwardly trying not to kick it.
I have it for the Mini (single). I don't really like it. It serves it's purpose but it is really really hard to push the stroller. It really throws the balance off but I could get used to that. My main issue is that it sticks out way too far and I don't have anywhere to walk. Also, I have to have my arms all the way stretched out (and I have long arms) so pushing is very awkward. We will keep using it because it does work, but we'll only use it when my older DS is really really tired of walking.