The Shark is an underwater rocket- hope your nerves are good.
I've seen a couple of these built up, and they run very well providing you ballast it very low in the water (i.e. have just the top of the sail poking above the water).
The optional goodies, apart from the power plant, are far from essential.
Infact, I'd say spend your cash on other things. A reed switch from Engel would be a good addtion, allowing you to switch the radio on and off without opening up the hull.
The only thing I don't like about the shark, is that it only has moveable forward dive planes. This makes it impossible to use an automatic leveller, which is invaluable on a fast sub like the Shark.
You could modify the hull to incorporate moveable rear vanes. This would be worthwhile I think.
Andy