There is a new product trying to get to market that seems to be very interesting and promising. However, they failed in their crowdfunding effort and I'm not sure if it stalled or the inventors are still trying to get it to retail.

It's called the Rescue Me balloon - a flare sized unit (6" x 2" dia.) that has a helium canister, an inflatable balloon on a 150' long fishing line tether. It also has a strobe light with a 7 day battery. I presume you set it off like a flare and aim it at the sky to deploy the balloon. It provides a visible SOS and light above the user.

Watch the video and tell me what you think. If it ever becomes available it would provide a welcome addition to a life raft kit. Being seen easier would definitely help the SAR groups to spot you. I do have questions about its durability and if you are in a heavy storm you may need to reign it in to prevent it from being lost. How strong is the mono-filament tether? How leak proof is the balloon? If it does leak and you are able to effect repair does the canister have enough extra helium to refill the balloon?
RescueMe balloon

The second link is to an article where it suggests the price would be about $75 retail.
https://gearjunkie.com/rescue-me-balloon-distress-signal

The third link is to the home page on KickStarter where they have better detailed photos and information.
https://www.kickstarter.com/projects/651668573/rescue-me-balloon

The fourth link is to the inventor's bio.
Craig Key's bio