I got the wacky walkr coupled version for Sophie and Syrus to walk them in a public park with a little more control. They were still only 6 months old at the time and I got the longest anticipating their growth. The trouble was they were still able to cross behind each other.You can not adjust the length. They didn't get tangled up but kept pulling one or the other over. The rubber band effect kept them pretty springy. Plus my kids are a bit clutzy to begin with.
I found better control with each harnessed and individual flex leashes. I could reign them in when needed or just cross the handles in my hands when letting them out to full extent and they crossed each other's path.
I don't know how the wacky walker would do with a single dog.
Hope this helps a little.