But since I'm aiming for 100% completion and so have picked up a shedload of missile expansions very early on, I can afford to spam missiles at baddies. Turns out it's ridiculously overpowered against the sentry drones - after a couple of seconds of tasering them they just drop to the floor. For added usefulness it immobilises the drone and stops it shooting back.
It gets better: you know that annoying invisible drone in the dynamo room that you can't lock on to? The wavebuster auto-targets it!