I don't know anything about them, but the covers look good and the website is geared toward readers and not writers. I personally didn't see any red flags, but I'd like to know what they're distribution is like. They're UK, so I don't think I've seen anything of theirs in bookshops here (US), but maybe someone from the UK can step in and tell us if they've seen them in bookshops there.
With PBs I think that would be the biggest determination on whether or not they're a good place to submit to.