This item is a koshihimo - with additional elastic bands added over a short part of the middle section of the himo.
This special himo is most used when tying fancier obi musubi, especially for furisode. By tying just one himo securely, you can secure three different sections of your bow by using the elastic bands. Very useful item indeed!
I find it most useful when tying furisode musubi onto myself. As I need to tie only one himo tightly at my back, I don't waste as much time struggling with all my himo and can concentrate more on the actual musubi.
I have a few magazine scans of this himo being used - I'll have to post them sometime :)