The IPS outperforms outdrives, surface piercing and jets as well. Granted sails and oars have better fuel economy, but they lack a little in the speed department.
(Just being a wiseguy)
Seriously though, this technology moved up from tugs to ships and now is moving down to the yachts. The only down side I see is in areas where soft bottom strikes are common (shallow bays) because it's certainly more expensive to replace a lower unit than to recondition a prop. Other than that I see this as the technology of the future.