Here's why they're not a good idea.
Let's break it down...
1. They make for a really really short lead. We know short leads suck, read why in our lead length blog: https://aussiepooch.com.au/blogs/news/leads-why-length-does-matter
2. Poop Privacy. Just like us, most dogs like to toilet in private. Imagine being tied to somebody and you get the urge to poop!
3. Different Gaits. Dogs don't walk at the same speed given the choice. They may be forced to walk or trot faster to keep up with their partner. They may be different sizes with very different gaits or one in more pain and have no choice at what speed they walk.
4. One dog reacts to a stimulus and the other can't escape. The second dog is more likely to react too. This can become a learned behaviour. Second dog may get several jerks as the reacting dog lunges toward the stimulus. A fight between 2 attached dogs is more likely due to a re-direction of frustration. Imagine the carnage if one dog got attacked by a roaming dog and the other cannot escape.
5. No freedom to sniff. We know sniffing is life for a dog. It's a calming activity which lowers the stress hormone cortisol in the body. The resulting shortness of a coupler lead does not allow each dog to read his environment with his nose. When one dog attempts to sniff her environment, the other gets jerked around.
6. No freedom to use body language to curve. Two dogs tied to one another don't for one on one greetings with another dog which could be a recipe for disaster. Polite, safe and successful greetings involve a curve and space.
We're your dogs advocate. Our main concern is your animal. We're all for solving your problems, but not if it's at the detriment to your animal.
We'll never sell something that makes your animals world suck, to make a profit.