Anybody ever use a walky dog, dog springer or 1-Running-Dog Bike Tow Leash?

[Andy]

Has anyone ever used them or something like them? It seems like a good way to bike with your dog. They seem kind of expensive though.
I like the 1-Running-dog bike tow leash but its pretty expensive. Anybody know of a cheaper one that works just as good?

Here are some videos i found on youtube.

Walky dog
http://www.youtube.com/watch?v=1-DkPrd3xLI

1-Running-dog bike tow leash
http://www.youtube.com/watch?v=m2tcKb2cgEE

Springer Bike Jogger
http://youtu.be/RhqdBKmIbYs

What do you guys think about it?