if there is any breeze at all you may have problems getting them over the spot you want to illuminate, but you've got a shedload so practise will make perfect. We used to use them a fair bit for night searches on the beaches and out on the tidal sand flats. On a calm night they are very effective ( and you should see what scurries out from under the Blackpool Piers on a summer's night clutching underwear to their bossom, when a bright light suddenly appears above them!).
The light they give off will likely be quite atmospheric for the job.
On a (very) windy night the illuminating para I fired from the end of north pier probably ended up lighting up the Pennine sheep by the time it had finished drifting.
And whilst not distress flares they will be reported as such, of that there is little doubt, but you've liased with the CG etc so jobs a good'un.
One word of warning LOOK UP! well two words actually but a certain cg team that we won't mention by name as I value my life did come very close to shooting down a light aircraft with a maroon fired on excercise. Adrian was thereafter known as Biggles!