Product review (5 stars): Easy to install - required for shared neutral circuits.
Easy to install - and required by NEC for circuits with a shared neutral.  Remove the dead man cover to the panel, cut power and disconnect the two breakers you want to tie together (ie ones with a shared neutral like a dishwasher and disposal), slip the handle tie between them and click both back into the panel. Give the tie a light squeeze with a set of linemans pliers and reinstall the panel cover and your done.