GRS are a share that are traded globally, unlike the ADRs that are receipts of the bank deposits of home-market shares and are traded on foreign markets. The GRS are fully transferrable — GRS purchased on one exchange can be sold on another. They usually trade in both US dollars and euros.
The main advantage of GRS over ADRs is that all shareholders have equal status and the direct voting rights. The main disadvantage is the cost of establishing the global registrar and the clearing facility.