If the F-DL
is a diffuser, what they actually do is slightly diffuse the highlights into the shadows, as opposed to a soft focus filter which slightly blurs the whole image. Diffusers can be very nice in posed portraits of ladies particularly, giving a nice flattering effect to the hair where there are highlights. They can also soften slight skin blemishes. A bit of a specialised filter really unless you have a specific need for one.
