The Bob Yak is the only single wheel trailer worth having in my opinion. We are closing in on 12 years with ours. There weren't any knock-off's when we bought our Yak, but there were a couple of European single wheel trailers that cost as much or more than the BOB. The Nashbar knock-off was first but I don't know if it is still made. There is another knock-off that I know of but I can't remember the name. What I know is that the BOB has a stated weight limit of 70lbs. but it is so seriously overbuilt we routinely exceed the limit by more than 30 lbs. I actually think they use the 70lbs. because that may be the highest safe weight for a single bike to pull without being overwhelmed. We pull it with a tandem. The cargo bag that comes with the YAK is not duplicated by any of the knock-off's and it matters. I would rather try to find a Yak used to save money than buy a knock-off. As cyclists the ONLY impediment to our forward progress is air resistance. A Lance Armstrong level cyclist struggles to achieve 30mph on level ground but with something to block the wind (air resistance) that speed would be 186mph. A Burley Travoy knocks a couple of mph off the top speed of an average cyclist. It isn't that noticeable in town but on a tour? Uh, I would think so! Lower two wheel trailers (the majority) still present several square feet of bluff afterbody to the airstream and two wheels where just one would do as well. Sorry, the single wheel trailer wins for aero efficiency and as a cyclist that is all you should care about. That it is also strong and light for its size is a plus.