I believe that slide up is thought characteristic of Purcell but not of the
earlier composers (e.g. Byrd). My intuitive response to ornamentation is that
it is always done to draw attention to a particular note. In the French style
the slide fill-in can extend to intervals of up to a fifth but must be used
judiciously (try filling in a sequence of descending fifths and notice how
tasteless it quickly becomes!) But it is never marked; the player just knew to
do that at certain spots -- le bon gout is VERY important in French style! For
the English style to have a specific mark for an ornament that was elsewhere
understood as a rule of practice, and otherwise not to have a mark for the
mordent, which is such an expressive gesture and apparently common to all other
European music of the period seems to weigh heavily in favor of the one-slash
mordent, unless a particular effect is acheived by delaying the entrance of the
decorated main note. With a mordent the main note is sounded first; with the
slide the main note does not sound until after the lower auxiliary has sounded.
Just my own thoughts on a developing personal practice.