The trailer hooks onto the back-wheel on both sides of the axle and fits wheel-sizes from 20-29-inches. Will haul up to 300-pounds of gear. The rig is adjustable up and down so the load stays level whatever size wheels you have, and you hook it onto the bike using simple thumb-screws.
The advantage of a trailer over a cargo bike are many. It means you can free your bike for everyday use, and the separate parts are easier to carry up to your apartment than a long-wheelbase bike. It’s also easier to carry large loads. Try balancing out 300-pounds on even a heavy-duty cargo bike and you’ll see what I mean. The Surly Trailer also comes with “DIY mounts all over it” so you can “Make your own bed, add some uprights, strap down your friends.”