I have an older Surly Big Dummy (with the curved top tube) so it was designed to fit all the xtracycle stuff. I was lucky to buy it secondhand with all the bits I needed on it, the only thing I've added is the front wheel stabiliser.
My u tubes were fabricated by really useful bikes, but everything else is xtracycle stuff. The pannier bags and U tubes are ace for carrying shopping, stuff or bagging and dragging another bike
It's running a hub gear which is great for being able to change gear when static. It's definitely more draggy than a derailleur set up though.
Ute's often come up on eBay, usually in 18in rather than 20in size. The only thing I heard about them is the 700c wheels put the load slightly higher up than on 26 or 20 inch bikes.
I like the idea of getting a hooptie but in practice it would make the bike much bigger to store. The U tubes, being low, don't take up as much space when trying to get past the bike in my garage, and I have a wide and curved stoker bar on it which both kids can hold onto when on the bike