Yeah, the fan is going to depend on how close you sit to it. In a typical living room connected to a TV, it's not going to be audible except perhaps in the dead of night with absolutely no sound being generated by anything except the fan. On a PC monitor that is just 1-2 feet away, however, it'll definitely be noticeable. It'll basically depend on how quiet your room is. Its rated at 28 db at 1 meter. So quieter than a PC and below the noise floor of most people's homes in the afternoons.
Then again, other than for testing why in the world would anyone want to put one on their desktop PC monitor?
Yeah it doesn't use much power. Anandtech noted idle at 2.45 watts at the wall and 8.82 watts at the wall when loaded with Prime95 + Furmark (IE - greater than anyone would likely ever load this up with). Youtube HTML5 streaming at 6.09 watts with Firefox and 3.55 watts with IE. Netflix at 3.25 watts with the Win 8.1 Netflix app. Pretty good all around. That is less power consumption while playing a video than my Sony A/V receiver in standby mode.
I believe Scott Wasson tried his out on a TV in his bedroom with it powered by the TV USB port.
If I got one, I'd likely just hook it directly into my A/V receiver, at which point it wouldn't matter how I powered it. If I took it on vacation I wouldn't even bother with a wall wart power adapter for it. If a TV didn't have a powered USB power port I could just use my phone's charging cable to power it. Then again, since I'm getting a Surface 3, I wouldn't need this for travelling anyway.
Regards,
SB