QUOTE(Ejtek @ Apr 9 2006, 02:33 PM)

Or just a good way of charging more money for less material.
Maybe I can shed some light here.
In terms of performance, I would say both are equal. Funny how all the comments saying "this or that is better" give no rationale whatsoever...
In terms of correct anatomical and ergonomic performance, in any shoe (especially a performance shoe like a football cleat), what you want is the shoe to be stiff in the waist (middle of the foot under the arch), and only flex under the ball of the foot. This is how the human foot moves. take a slow-motion step and watch your foot, you'll see.
If the shoe flexes in the middle, where your foot doesnt, it can cause pain, discomfort and poor performance. If you foot flexes in the middle under the arch.....go to a hospital, you've just cracked about 10 bones!
I would imagine, that the split sole design originated from a creative designer trying to make a boot look lighter. Indeed it does. The actual weight difference, however, is probably very small though. If a boot uses a split sole design it must also have very good reinforcement inside the shoe to prevent the above mentioned flexing problems. Usually this is done with a semi rigid midsole.
This midsole (part of all boots) can be made from a variety of different materials, at different costs. For the cheaper boots, with the least stiffness required (entry level boots with one piece outsole) this is usually a cardboard type material. I should also mentioned that some top boots with a hgh quality stiff outsole design may use this type too.
A step up from this is molded insole, which can be made from either PE, TPU, or nylon. This provides more stiffness, can better fit the foot shape, and is of course more expensive.
The top choice, is of carbon fibre. very $$$$$$, but very stiff (note however that carbon fibre does completely crack in half if flexed beyond a certain point).
of course, like the F50, or tunit, this midsole stiffening property can also be designed into the insole...
hope you enjoyed today's lesson in shoemaking.
cheers,
R