Looks like a variation on the SOLAS survival at sea that's been around for decades.
Let's not confuse stuff here. SOLAS is a set of standards (Safety Of Life At Sea) for various equipment and requirements for equipage. Contrary to popular use, there are no SOLAS Regulations or Approvals, that is all done by national authorities (e.g. U.S. Coast Guard for the U.S.). SOLAS doesn't really have anything to so with Solar Stills per se, but they could theoretically be used to meet various SOLAS standards for fresh water producing devices in lieu of stored water in some circumstances.
Completely ineffective (as I understand the matter) at sea because of wave action.
Actually they can be effective, but are temperamental and won't work without sunny skies and/or in heavy seas (usually accompanied by bad weather anyway). Read
Adrift by Steve Callahan for a story where they saved his life, albeit with careful tending and improvisation on Steve's part.