Slabquest - I have the hour meter/tach unit and love it. It really does help to keep track of maintenance etc. It's also great for logging rpms that you were running when hooking fish. Speed from GPS and depthfinder is good but not nearly as accurate as rpms.
The nozzle I'm referring to is round like a prop guard but it's quite a bit more involved. It is about an inch larger in diameter than the prop and mounts with 6 bolts to the cavitation plate. What seperates it from a prop guard is that it's about ten inches from front to back with the front being larger in diameter than the back. This concept produces a compression of the water as it's sucked through the propellor thus providing more thrust. Propellor nozzles have been used on tug's for years.