There have been plenty of personal submarines for the ultra rich, but most of them will only putter along at a few knots. The SeaBird manages to scream along at 40 mph, but there's a big catch.
Most personal submarines have a small electric motor driven propeller with limited power to maximize battery life. With the SeaBird, you are pulled along by a boat on the surface, at the end of a 400 foot tow line.
There are electric motors to adjust the various rudders and flaps, allowing you to control your depth and direction to some extent. Maximum depth is 300 feet, presumably only when the surface boat is stationary.
Manufacturer AquaVenture says you can stay submerged in the SeaBird for up to three days, although I think that would be a challenge for anyone with even a hint of claustrophobia.
AquaVenture says they are taking orders for the $210,000 SeaBird now.