'Brick-nade' Pros:
-forces enemy infantry to be suppressed and pins them down when directly hit.
-sometimes, 'brick-nade' will force enemy infantry squads to retreat.
-rarely, it would force individuals in an enemy infantry squad to rout, essentially losing men (as shown in the GIF).
-can be thrown on nearby enemy infantry while garrisoned (best against flamers).
-doesn't need munitions.

'Brick-nade' Cons:
-slow throw time.
-really long ability cooldown.
-horribly inaccurate.
-thrower highly exposed to enemy fire.
-has virtually no damage.
-piss poor throw range (almost as same as penal's satchel throw range, albeit 'brick-nade' has slightly larger radius).
-slow projectile speed (same as penal's).
-doesn't work on enemy infantry that are garrisoned.
-obviously won't work on vehicles.

Conclusion: Best used in ambushing up close. With proper support, tactics, and clever use of smoke, this ability will be an important asset in taking down the toughest elite infantry units your enemies had.