I discuss the steam part of things here.
I'm thinking that it will actually cook the mash and cause problems that way. I'm guessing that the steam is not going to be under pressure so it may have difficulty in clearing flour that is usually present in the mash. A manifold is more rigid, will help with less localised release of heat and can be modified in the size and amount of steam delivery points.
The steam did not cook the mash. The heating is very gentle, but yet effective. The steam bubble doesn't immediately burst, it travels through the mash.
The steam IS under pressure. Up to 15 PSI if you want it to be.
A solid manifold is necessary to prevent the manifold from floating.
See the steam thread for details and further discussion.