Many of these special tools have work-arounds or just serve to make the job faster. So, unless you have the $$$ to burn or find some really great deals, you may want to take a hard look before you buy. Scubapro is mighty proud of their multi-tool and there are many alternatives. Soft jawed pliers (or even a rag) will replace the spline tool needed to remove those damn scubapro hose connections. A pair of bent nose needle nose pliers will do an adequate job as an alternative to a pin spanner. The ambient chamber on a BP may require some tailored ingenuity but can be done without the special tool. I found a pin spanner on ebay that works fine. One of my first projects was to modify a 1" socket for use as a yoke nut socket. (
Homemade yoke nut sockets - ScubaBoard Gallery) The one on the right is a 1/2" drive socket with a 1/4" drive insert for use with older style lighter yokes. I did buy the picks, a bullet tool (both pretty essential) and the Mk20/25 assembly tool. I'm sure I could have done without the assembly tool.
Good luck.