Ok, so I may not be getting harder in my pictures.
It is indeed a DM 51. You are right in it being both an "offensive" and "defensive" device in one. The device is entirely made of plastic with the exception of the fuze and spoon. This device is arguably the single most effective "defensive" grenade anywhere in the world. That is until the Swiss introduce their version of our M67. The grenade can be connected to other DM 51's end-to-end to make Bangalore Torpedos and cluster charges. The plastic matrix with balls vaporizes upon detonation sending the balls out in all directions.
Some specs:
Weight: 435g
Fuze assembly weight: 64g
Fragmentation jacket weight: 290g
HE filling: 60g of Nitropenta
Number of balls: 6500
Size of balls: 2-2.3mm