They are very good at their main purpose, which is to support tank formations in combat. However, PzGs should never be trusted with clearing a forest of armor, as their AT weapons have a long reload and fail at close quarters.
Panzergrenadiers do good on their own as well. However they are not great as a defensive infantry, rather they are better in the offense. Many players make the mistake of using them as they would use basic infantry.
The Marder offers generous tracked transport, AA/AT capabilities, good armor, and good speed, allowing them to be a good response to any threat.
The term Panzergrenadier originated in the Heer and SS during the Second World War, and was applied by the post-war West German military, the Bundeswehr, to the mechanized infantry units that make up the backbone of the army to this day. Armed with G3 rifles, Pzf44 or (post 1993) Pzf3 light anti-tank weapons, Milan guided-anti-tank weapons and MG3 Medium Machine Guns, the Panzergrenadier were a powerful force to be reckoned with.
They originally operated from M113 APCs but switched to the Marders as they came online.