The one characteristic about diopter lenses is how powerful they can be when used with long focus lenses. A 1 diopter lens will focus whatever lens it is put on at on at a distance of 1 meter. Therefore, if a 1 diopter lens were put on a 300mm lens, it will be focused at 1 meter, a number 3 lens will focus a 300mm telphoto at approx 13 inches.

It is very doubtful that even the very best of these closeup lenses will fully equal a fine macro lens. It is also true that for the investment good closeup lenses do add a goodly measure of flexibility to you kit.