So, let's get this cleared up already so it's not too OP and can be tweaked sooner:

Currently I have in mind a thief-type character, who used his cloaking device to steal what something called an Anti-Matter Particle Cannon, or AMP Cannon. It would release streams of anti-matter, and as you may know, when matter and anti-matter interact, annihilation happens, causing a huge release of energy - an explosion. AMP Cannon is extremely accurate and has massive range, but has a very low rate of fire, as it takes a few minutes for it to cool down after each shot. The released stream also makes a distinct screeching sound and reveals his position. While the ammunition would be unlimited (because you wouldn't find special energy cells for a super secret prototype weapon anyway, so the weapon being limited that way would be quite lame), the gun is quite large and heavy, making concealment nearly impossible. Though there is a special large suitcase for carrying it, it still quite stands out. Also, it could not be used in short range fights, as the explosion would kill the shooter too.

As for the second device, it would be a predator-ish cloaking device.