I have AF tubes. I've never had a problem with them. If you use a reverse ring adapter, you won't need AF tubes. If you have lens that have both manual aperture and manual focus, you don't need the AF. I'm not sure what you are referring to for the locking mechanism, but AF and non-AF tubes should have the same attachment and lever to lock and unlock the lens when turned into place.
My lens have manual focus but not aperture. I had to get AF tubes and when I got a reverse ring I made sure to get the one that came with a manual aperture adapter.>>3183319>>3183324
The teleconverter magnifies what is already there. Since it also pushes the lens further away from the body it shortens the working distance between the subject and your lens. This darkens the image and since there's extra glass the sensor looks through, it will add some sort of aberrations depending on the quality of the teleconverter's glass. If you have an expensive lens and cheap teleconverter, it means you are seriously degrading the quality of your lens because of the cheap glass in the teleconverter.
If you have a telephoto lens, you can use these things to take macro shots from 6 feet or so away from the subject, depending on the lens. That's great for insects that are skittish, like butterflies, tiger beetles, big roaming spiders, etc.
If you really want extra macro, try using 2 sets of extension tubes before paying for an expensive teleconverter. That way you'll have no extra glass at all between your lens and the body. It is a cheaper method.
Now check this image out. These are not cropped images, I just reduced them from 6000x4000 down to 1024x683 for this example. What I did on the right image was to take my 68mm extension tube and add a paper towel tube between it and the camera lens. I put the aperture adapter on the lens so the aperture could be wide open. I had the body on the tripod and held everything together with my hands, hence not quite in focus/blurr.