A couple of points:

• What does the foil under the batter head do?
• Ultimately, what would this be used for?

My guess is that the foil helps imitate that "split-your-eardrum and yank-it-out with pliers" crack that drum corp players have loved in the last couple decades.  And it would eliminate ring, too. (Having no eardrums also helps with the ring problem).

KEVLAR heads!?!  whoah....  heh... wow.

The foil adds a nice crisp crack to the drum.  It does eliminate some ring.  Pretty much, this is just for another sound on your set.  It sounds good in a lot of fills.  I personally like Kevlar drum heads.  If you don't overtighten them (like drummers usually do), they sound just like any other heads but are stronger and last longer.  The reason they are used for marching is because of the heavy sticks and loud accents the drummers have to put on them.  Anyway, it adds a great sound to your set.  We've all heard some songs that put in a little marching transition to add mood, haven't we??