From what I can tell in other news groups it either works or it doesn't.
Some people reckon supermarket petrol is rubbish, others like me have never
noticed any difference. There may be a long term benefit over several tens
of refills but it may also be that any benefits in terms of fuel economy
might be undercut by cheaper petrol.
Certainly in my motorbike fuelling with standard unleaded or superduper
unleaded makes not a hap'orth of difference.

Just like other High Octane fuel (Super Unleaded, BP Ultimate) it does
nothing whatsoever unless your engine is specifically designed to use it
(ie, high-performance Japanese cars).

Octane rating is simply resistance-to-knock - the higher octane the fuel is,
the higher the compression ratio an engine can use before detonation occurs.
If you're not running said higher-compression, then there's nothing to be
gained.

It's just damned expensive for bog all gain. Unless it's for a Ferrari