My reading of 18.07 safety regs says USCG Approved is for flares OK? Normal ambiguous ynz English, but pretty sure intention is there.
If you're worried about how well your electronic flare floats, throw your pyro one in the water as a reference point.
I got an electronic one and I would far rather have that than a bunch of of dodgy fire starters
18.07 The following distress signals must be carried in
addition to those in the life raft.
(a) Four red hand flares, additional to those in the
life raft.
Two red hand flares, additional to those in the
life raft.
OR additional to those in the life raft, a LED
or laser flare, which has been approved by
the current international convention for the
Safety of Life at Sea (SOLAS), United States
Coastguard or Maritime New Zealand.