I doubt anyone would bother using it, not anyone used to the class already atleast. Not when they can just strafe corners going D-mouse1-A-D-mouse1-A-D-mouse1-Mouse2 to take out any sentries, and still have a fully fledged assualt weapon to bare afterwards. Especially since i would only see it as a one off recharge thing to stop it from being abused. Although it would be awesome against a defencive position stuffed full of heavy medic combo's.
I'm hard pushed to imagine an alternative to either the sticky or grenade launcher. I imagine they might just alter the dynamics of the weapon like Natascha. EMP stickies or something. They damage buildings, even through walls but only effect buildings, not players. Or something.
A Boojum Snark: Don't listen to grazr he is probably drunk