I like to give my dogs the flexibility to explore on walks, so a longer 15 foot, retractable tape leash is great. The Flexi(tm) leash system is a great design, and it has a built-in rail for accessories. I purchased the Multi-Box in order to take dog waste bags along. This accessory frustrated me as it always popped open and let the bags unroll behind me. I decided I could do better and put my FreeCAD skills to use. This design works much better for me. I hope it can help you as well!