PJ, yes, you can use a fully battened sail on a Prodigy. It is easier to control than a soft sail. But no, don't try using a harness until you have got your basics right. Many inexperienced sailors think that a harness will help them learn faster. This is just not true. They frequently try to hook on when the wind is too light and then try to get into the footstraps. The board immediately turns into the wind and they fall off. The harness is to take the strain off your arms when the wind gets too strong.
The reason why I would advise beginners and intermediates against buying a board without a dagger-board is that these boards are designed for planing at speed. When not planing they are difficult to sail upwind. The Prodigy is a very good board to learn on and to get your basics right. After you have learned to handle that board in most conditions and you want to go for speed then you can think of going on to a slalom board/formula board, but not before.
is it possible to use a cambered sail with a longboard?
