It does work great with my dachshund, haven't tried with the big ones yet. I did have to install it upside down so it wouldn't be in the way for pedals (works really good that way tho) and I had to use 2 rubber mats instead of 1, that it came with,so it wouldn't move on the frame- first was between frame and the plastic thing and second one was between the plastic and the attachment. But still don't forget that your dog must know how to run beside a bicycle to a some degree before!
I used one of these for years on bridleways and forest tracks with my Springer Spaniel. It is brilliant but I would say it should always be used with a harness, not a collar; you should be aware of setting a sensible speed for your dog (i.e. his normal "loping" stride) and make sure you stop for water and toileting; it is not safe to use where there is traffic.
just started using this and my dog has adjusted very quickly. my dog did get distracted and the spring worked very well although we were not going at a fast pace. im very glad i purchased this as now my dog is getting allot more exercise than just going for walks.
I have also owned 2 of these for about 10 years they are not suitable for all dogs as some of them just find the idea of getting that close to the bike wheels to much.But if they like them they are great as you can let them run.Keep them on a very short lead or they will go under the frount wheel it does NOT stop them pulling but it does give you a secound to respond when they do so you do not end up on the floor.A WORD OF WARNING if your dog is not used to lots of exersize dont sudenly start taking them for great long runs. My springers used to find a mile or two running at there own pace plenty but they loved going out on it.(my present dogs are to old or think it is the most scarey thing ever and dispite seeing there parents use it and being walked with me pushing the bike will not have any of it.)
we bought this for our weimeraner as she needs lots of exercise and it has been a great success. Only a couple of points, she is still able to pull with it - especially if she sees another dog/animal so you need to be aware of that. Also even though we tied the lead cord in a knot she was supposed to be unable to pull open, it did so very quickly. We remedied this by attaching a short lead and this works well. Also worth pointing out is to check your bike before purchasing, as this doesn't fit all modern bikes- you need a good length of upright bar under the saddle to fix it to.