HDVdiver
Registered
The drawback is that you need a dive canister for every plb I've seen. Which cost as much or more than the plb itself and makes it much bigger.
That was the case a few years ago when the only available purpose built canister was the large, heavy and expensive McMurdo FastFind PLB Dive Canister. Also, being machined from aluminum I always worried that the threads on my unit would corrode and prevent opening in an emergency. That old clunker has now been converted into a cave diving light canister...
The new generation of very small PLB's has allowed several manufacturers (that I'm aware of) to produce equally compact and cheap (around $100) purpose built PLB dive canisters. Being made of tough high impact plastic they are totally maintenance free. Most will easily fit into the average BCD pocket or a technical pouch.
If you still find carrying a small canister a hassle, Breitling offer their beautiful looking PLB wrist watch...at $15,000 a bit more expensive than a canister+PLB...