Well, the Invisibility Cloak covers a wider range of wavelengths, so unless the players have access to radar or x-ray, they're going to have quite a hard time identifying where the wearer is by sight alone, at least according to how I read the rules. There's also the added advantage of movement and such. It's also [i]very[/i] powerful. I threw the NPC Files Ghost-assassin on my players as a single encounter and... Well... It killed two players and heavily wounded a third, blew a hole in their spaceship by accident, and they never managed to land a single hit on it - they only managed to kill it by ramming it against the ships interior hull repeatedly until it was dead. And then continuously for another two hours, because they couldn't tell if it were dead. By the description given in the rules, it seems that the Invisibility Cloak is passive, so it gives it effect without being powered, while the Chameleon coating/cloak/skin has to be actively kept working. It was, to be honest, a little more deadly than I had expected the encounter to be. One of my players swore that the next time he designed a character, it would have echolocation.

My question would be why wifi waves are not blocked?

I'd interpret it as the Chameleon is like active camouflage in Halo, while the invisibility cloak is more like the thermo-optic camouflage from Ghost In The Shell. The chameleon might be running on an image processing type technology (Like holograms maybe?), so if you move too fast, you overpower it's refresh rate and it creates a shimmer effect. While the Invisibility Cloak might be using something more like meta-materials, so no image processing is required.