First, I think it is not really traditional enough to talk about on the forum.
Second, I know that having to remove the cap, pry out the spent primer, install the new primer and then screw the cap back on takes a lot of time and it is a PITA to do. Especially if you drop the cap into the pine needles your standing on and have to spend time trying to find it.
I don't doubt that using it will make a much hotter, more powerful flame than a standard cap but unless your shooting something like Blackhorn 209 powder that is made for those guns we don't talk about, a more powerful flame isn't really needed if the nipple and flame channel in the gun are clean.
If a more powerful percussion cap is needed, the #11 Mag caps will usually do the job.
(I can't imagine someone wanting to spend over $30 for one of these Mag Spark things like the one I saw on e-bay.)