Hi Sharkman,
On all of my (rec only) dives I carry a safety sausage- the surface type. Probably a better idea is to add on the string due to the greater versatility.
On my 3 trips to Coz, I did see, on occasion, a DM deploy one during the safety stop. While the "bubblewatchers(?)" on board the dive boats were great at tracking the divers, the sausage can help. On those dives where the DM used one, the boat was "ready and waiting" when we surfaced.
I'd say bring one along, it can't hurt- especially if you were to get separated from the DM- it can, and has happened. Just be careful to not overinflate it, if you are letting it go from the 15' mark, as the air volume will increase on the way up.( I saw a "popped" one floating on the surface-though not in Coz.)
Good luck,
Mike