You could do a search on them, but to explain why not that many people have heard of them, they specialise in "built in at construction" gigabit broadband networks, usually for multi-occupancy buildings or estates of apartments. They install under contract to the developer, and that gives them a virtual monopoly on ISP services because nobody else would risk trying to retrofit FTTP into apartment blocks already served by a gigabit network. So no real need to advertise at all.
Having worked with developers on a similiar (non telecoms) concepts, I wouldn't be surprised if Hyperoptic have to pay a big fat wad to the developer for the right to do this, then add that to the costs served to almost captive customers. Headline pricing for Hyperoptic doesn't actually look at all bad, but I suspect that their costs are far lower than anybody trying to build FTTP by retrofit, there's no marketing costs of significance, and the churn is probably tiny, so margins are probably very healthy (until they're bought by some slimeball corporation and the M&A costs get added to the bills).