Shoot a SOLAS off, you'll be amazed. They don't take up that much room. We were given a bunch from a company that certifies life-rafts so you can get them for free with a bit of work. I like the fact that it's one piece and is incased in a waterproof housing. In an emergency I think it would be easier to use with less fumbling.

I'd say keep the gun you have and keep the flares up to date for the USCG. Purchase or get a few SOLAS and don't replace them when they go out of date. They'll be good for 10 or more years.

Pains Wessex flare video http://www.pwss.com/Videos.aspx