Don't actually know what I am in favor of; however, my kit came with the foam blocks and instructions to use the hysol to coat the foam after it is formed to shape. So I used what I had.
Pretty much the same deal Lowell is talking about; and, epoxy primer/aerothane over the whole works resulted in a very nice termination & finishing of the flaperon.
BTW - the aluminum skin of the flaperon is more easily dented than the end foam/hysol finished cap.
The end result is pretty much a matter of how well a person does their bodywork on the end cap before it is painted.
Sincerely,
Dave S
KF7 Trigear
912ULS Warp Drive