The BlueLine 8''/20cm w/ Slider & 4''/10cm Coupling Strap

I really liked them, they seem very well thought out and of very good quality.

We use a Sprenger pinch collar for walking and a regular collar in the house for our German Shepard. The Blue line coupling straps hooks are clearly too small.
They barely fit on the pinch collar, and they do not on the ring of the other collar at all. The hooks are smaller than the way they appear in the picture.

The Blue Line coupling strap is a great idea, far less cumbersome than a carabiner between the two collars. My only issue is with the clips themselves. They are smaller than needed for a medium to large dog and can stick when unhooking from the prong swivel 'd' ring.