I dug a bit and found reviews in Spanish sites and from there I got to the standards used.
These plastic optical fibre to ethernet adapters are the first implementations (AFAIK) of 1000BASE-RHA defined in IEEE 802.3bv-2017: "Physical Layer Specifications and Management Parameters for 1000 Mb/s Operation Over Plastic Optical Fiber". The spec defines the following versions:
1000BASE-RHA: 1000 Mb/s using 1000BASE-H encoding over duplex plastic optical fiber cable and red light (approximately 650 nm) wavelength transmission tailored for home network and other consumer applications
1000BASE-RHB: 1000 Mb/s using 1000BASE-H encoding over duplex plastic optical fiber cable and red light (approximately 650 nm) wavelength transmission tailored for industrial applications
1000BASE-RHC: 1000 Mb/s using 1000BASE-H encoding over duplex plastic optical fiber cable and red light (approximately 650 nm) wavelength transmission tailored for automotive applications
The plastic fibre used is quite thin: a pair of 2.2mm cables with a 1mm optical core (for a total of 2.2mm x 4.4mm) . They are very flexible and it appears that they are easy to pass through pre-existing communication and electrical conduits that are very common in Spain and probably other parts of Europe.
The specs are for 1000Mbps for up to 50m cable runs. From 50m to 100m the system switches to an Adaptative Bitrate (ABR) mode
One review I found published the following results measured using iPerf:
-40m installed passing through 35m of conduits containing 220V electrical cables: stable 940Mbps both ways
-60m cable still in the roll: stable 940Mbps both ways using ABR
-75m and 80m cables still in the roll: around 150Mbps both ways using ABR
-100m cable still in the roll: around 95Mbps using ABR
Several other reviews showed similar results over 20 to 50m of installed cable.
The costs are around €1.5 per meter of the plastic optical fibre and €62 for the simplest adapter (1 optical to 1 ethernet). They also sell 1x3, 2x3 and 4x1 adapters and a SFP to POF adapter for €35. The prices are VAT included. Not cheap, but not terrible expensive either.
For the weekend I will buy a thin flexible fish tape and see if I can find a good route from my router to an upstairs room through a mix of electrical and communication conduit. If successful I might give these gigabit POF adapters a try and report back.
One more thing: multi-gigabit versions are being developed so we might get 2.5Gbps, 5Gbps and 10 Gbps versions in the next few years.