Not seeing their books in bookstore is not the big test over here that it is in the US. There are far fewer independant stores and it is very difficult to get your books into the chains.
FWIW they look legit
They look like they only have ten ISBNs. They look like they've been in business for less than a year. They look like among their six authors only one has ever published before (and that one previously published specialized non-fiction; her book here is a novel).
Yes, it's difficult to get your books into bookstores -- if you're trying to do it yourself. Distributing your books is the publisher's lookout.
I don't imagine that bookselling is so much different in the UK that most commercial books are sold anywhere other than bookshops. If they aren't sold in bookshops where are they sold?
Your best bet is still to see which publishers actually get their books shelved and start by querying them.