I think they do a good job at hiding that ugly plug, thats a plus. But I was always worried about them holding in the heat on the TB itself, and causing issues with it. My fears don't seem to have come true. At least I haven't heard of too many issues that seem to be caused by heat. But I still haven't put one on. I do try to hide stuff like that plug, but it seems the cover draws attention to an area, that really isn't an issue unless its a very custom kind of bike.
I think the chrome cover is better than staring at the throttle body itself. As far as the heat goes, it isn't totally enclosed. In my case, any air that bypasses the filter is directed towards the throttle body by the flare at the base of the air cleaner.
Didn't even know they made such a thing. Now that I do, I don't want it anyway. I don't think the TB is ugly, but I guess that's a judgement call. Nothing against chrome, I've added some myself. Just don't like to cover something for the sake of covering it.