There are two sorts of FD-EOS converters;
Simple mount converters that allow an FD lens to be mounted on an EOS body. I have one of these for macro work but the ability to focus to infinity is lost.
To allow full focus range, there are converters with a lens element built in. This is where cost versus quality becomes part of the equation. If the conversion lens is optically poor then it really is a pointless exercise and I don't expect that the £15 ebay ones will do justice to a 10Mp body and an FD (L) lens. Canon used to market their own a few years back but it has long disappeared from the catalogue.
Bob