I have something similar for my point-and-shoot camera and it is basically a wide-angle filter. If you took your lense and attached a red filter, the lense would see everything with a red tint. This thing seems to do the same sort of thing, in that it allows your lense to see more of everything, but the lense still operates in the same way.
I think it is misleading for them to say its got AF because if it is a converter filter as it looks to be, then your camera is what is providing the AF, and this thing isn't doing anything accept changing your field of view (which is still kinda cool...I love my wide-angle converter and use it often). As far as the price goes, it's not bad. I paid $40 for my dinky little filter, and it only has two elements.
One caveat is expect serious amounts of vignetting depending upon the lense that this is mounted to. On my camera, when the lense is set to its widest view, it picks up the inside of the filter giving me rounded corners on the shot. Granted, I still see much, much more with the converter than the camera by itself, even with these dark corners, so I just crop them out and go about my business.
If you use this converter to shoot buildings, trees...well, almost anything, you'll notice a fish-eye effect. You can fix it is photoshop with some add-on barrel distortion correction filters.
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