1: It looks cool, a visual theft deterrent.
2: It will stop morons from yanking the seat out just to be annoying:
1: The wafer tumbler lock is easily picked in the matter of 3 seconds or less.
2: It comes in limited sizes.
I like the product, but Pitlocks are a far better solution to this problem. Pitlocks have a far smaller attack profile, can't be easily "picked" with a paperclip (though not 100% secure), and protect not just the seat post, but both wheels and stem, without needing an additional key to carry around.
Looking at the design, here are my recommendations:
1: Ditch the wafer tumbler locks. Go with Medeco, and some type of cover over the cylinder. This will up the ante for picking the lock to accomplished locksmiths.
2: Make a similarly designed set of lockable skewers for the front and back wheels. Sell these and the seatpost lock as a set for around $50-60.
3: Consider making exposed parts out of a harder metal.
Now, this would be a package that would secure on the par with Pinheads, Pitlocks, and other locking skewers, and offer a LOT more different keys, as well as master keying, to allow bike rentals.