I've never used these patterns but I think they would be ideal for head and shoulder risers that are taking nymphs UNDER the film rather than in the film.
I do have an issue with naming them "emergers" which means to me that the actual process of the breaking through the nymphal shell has begun. These flies are usually fished during emergence, but they seem to me to be "suspender" nymphal patterns using the parasol to suspend the flies rather than the classic greased leader method that is used.
The greased leader is a better option in most instances rather than the parasol, and I think that is why the parasol has remained a "niche" pattern where a more visible leader is detrimental.
The greased leader was written about by Gary Borger in his classic book Nymphing
, and is explained by Jason Borger in the link below. The advantage over the parasol is that you can vary the depth of the fly without changing the fly, and the fly lands more gently.
"A greased leader certainly does allow you to suspend flies at pre-determined depths"
The disadvantage of the greased leader is that the leader itself is more visible. So if I were to use the parasol "emerger", I would use the sunken leader technique to remove the impression of the leader on the meniscus. Rub some Snake River Mud on the leader to "degrease" it.
I wrote about the need for degreasing leaders with picky trout earlier. Go down to the middle of the page below.
Light tippet or not...