Mario Maccaferri, in addition to being the luthier behind the Selmer Archtop Guitar, was a pioneer in the production of plastic musical instruments not meant as toys and even started his own plastic company, Mastro Plastics to make them. Much has been written about him on the Internet so I won't say a lot here. There is a link for further information. 

Maccaferri and his Mastro plastic firm produced a number of brands of Ukulele and Banjolele, (plus Guitars, Drums and all manner of other instruments), with production of the Islander starting in January 1950, (the Islander Deluxe Soprano Ukuleles are reputedly the best plastic Ukuleles made). It is only the Islander range that has the Maccaferri name on them the rest just have Mastro or sometimes nothing beyond the specific branding, but other brand names used by the firm include TV Pal, Playtunes and Ukette, (more used as another name for the Mini scale). As well as having their own brand names. They also made a number of promotional models for pop stars, (most famously the Beatles in America), Cartoons, (like the Dick Tracy Sparkle Plenty), and TV programs, (like Romper Room). The Islander, and the other ranges came in Mini, Soprano and Baritone scale Ukuleles and Plastic Soprano Banjoleles.

One of the things that differentiated Maccaferri Ukuleles from the other ones of the time is the number of moulded parts used to make up the instrument, 8 as oppose to 4 for the Emenee and 2 for the Fin-Der. Plus Maccaferri/Mastro Ukuleles have a zero fret whereas the other plastic Ukuleles of the time don't. Even though this is the case, and Fin-Der was the first to put in for a patent for a plastic Ukulele, Maccaferri still fought and lost two court cases with Emenee over copyright infringement?

The Maccaferri designed Ukuleles often have a sticker says Styron, (describing the brand name of the plastic it is made from), on the front. It looks ugly but is is an original feature. 

In 1969 an aging Maccaferri sold out to Carnival and production stopped. 

I know there was a relationship between Maccaferri and the UK plastic firm Selcol - well Maccaferri had worked with Selmer to develop the Selmer style archtop Guitar before WWII; and Selmer owned Selcol. I don't know how direct it was after the war but that it must still have been close as Selcol produced a number of pretty much identical Ukuleles in England (and had the Beatles contract for the UK).