FD lenses are designed to sit closer to the film/sensor than EF lenses - so there is no adapter that can just place the lens in the correct location (because the correct location is inside the camera where the mirror is).

This leaves us with to options:

1. Adapter that places the lens farther than it's supposed to be - this has the same effect as placing the lens on a macro extension tube, you lose the ability to focus to infinity and from what I heard you are likely to lose the ability to focus behind macro range.

2. Adapter with a lens to corrects the distance difference (like the adapter you linked to) - so you just take an old lens (that is not as good optically as the new ones) and run all the light trough a second cheap lens degrading image quality even more.

So, if you mount FD lens on an EOS camera you have a choice, you can have an impractical focus range or bad image quality - and as an added bonus you also lose auto focus and other niceties of your camera.

If you want to use cheap old lenses you should choose lenses for a mount that has an adapter that can place the lens at the correct distance without optical corrections, basically and mount with the distance grater than what EF uses (you can use this list) - but you still lose a few decades of advances in camera and lens technology, don't expect the old cheap lenses to be nearly as good as the new expensive lenses.