On a mobile unit, not that great. They can add some ranged firepower to infantry units (mounted on light support vehicles) for dealing with pillboxes or other small fortified strong points from outside the range of conventional infantry support weapons.
I've also tinkered with the idea of a boom-box: a rocket pack in a box that can be dropped off by a truck or VTOL somewhere and quickly camouflaged. Firing would be accomplished by either a trip-line device or a wired remote routed to an infantry squad.
