I use the double Davy knot quite a bit. I have had problems with the single Davy knot slipping, especially if the wire of hook eye is large relative to the size of the tippet. The Davy knot depends on a small wire hook for it to cinch up properly. I found it a little fiddly to tie until I came up with a method of weaving the tag end of tippet through to form the knot.

Ted