Hardware is based on our existing
bluebuddy data logger with some firmware modifications to support this new "Electronic Leash" operating mode (a scuba variation of Apple's iBeacon

)
App is a brand new one (it will be available for both iOS and Android devices)
First - excellent idea! BRAVO
Is your thought that each individual diver will buy one, or that the boat buys a supply and loans them to divers?
For this to gain traction and become ubiquitous it has to be cheap. I know that many are buying the Nautilus Lifeline, both as individuals or as dive op owners to loan out. However, Nautilus probably have less than 1% market penetration. At $250 each, a Nautilus Lifeline is a noteworthy expense for individuals or those equipping a boat.
You have to get much higher market penetration to make it successful. That means it has to be inexpensive. Very cheap, like
tile cheap. It sounds like you are leveraging an existing product and modifying to add this new great functionality, which is a very low capital investment for you. However, does it result in an inexpensive point-of-sale? Will the incremental volume you achieve drive your BOM low enough? If not, maybe you should entertain a cost-reduced single function type of product that only does one thing. Maybe that's what you are doing, and I'm not telling you anything you have not already considered.
Anyway, I think it is a great idea. I hope it takes off. I'd gladly buy one if the price was not painful and I knew the dive boats had adopted the tech.