There are two types of FD to EOS adapters....those with a lens element and those without. If it doesn't have the lens element, then you won't be able to focus to infinity. If it does have a lens element, then your image quality is subject to the quality of that lens element.
And the problem seems to be that most of the adapters with lenses, are not the best quality. Plus, there is the added difficulty of using a manual focus, manual aperture lens with a camera that was made to control those automatically.
So unless you have some really, really good FD lenses...the usual advice is that it's not worth it.