I was more interested in reviews of them as publishers: how they're marketing, what's their distribution level, how do they handle royalties, how do they treat their writers, etc.
Over here, they have a distribution and marketing partnership with Osprey (a small but well-established non-fiction house) which seems to be getting their books into the book chains; in the US they do something similar through Random House. Ebook versions are available from their website and on Amazon Kindle.
They also arrange book signings (generally only in the author's home country), have their own podcast hosted by Mur Lafferty, blog and tweet regularly and encourage their authors to do the same. All in all I think their marketing is at least as good as any big house's SF imprint.
I have no idea about royalties, but I imagine they are industry-standard. I do know that when it comes to translation rights, if you don't have an agent or your agent doesn't handle non-English rights, Marc will act as your agent in this respect (which is why he attends the Frankfurt Book Fair). He's been in publishing a long time, and no doubt has lots of European contacts from his days with Games Workshop.
I only know one of their writers, Mike Shevdon, but he seems pretty happy with them. My dealings with them so far have been very friendly, and that seems to be typical of their management style. Sure they're in the business of making money, but they also seem to want to make the process as much fun as possible!
I recommend listening to the first Angry Robot podcast, which is an interview with Marc and Lee, otherwise you could be in for a culture shock
RE UK vs. US publishers, I'm glad to hear they're still accepting multiples on partial submissions. For US genre publishers, they generally want to see the
whole thing in the slush pile, they want an exclusive on it, and then it sits there.
Well, so few publishers are open to unagented submissions, I haven't looked into it, TBH. If you can find another UK publisher with an open slushpile, I would check their submission guidelines.
Make sure you check Angry Robot's, too. They are very specific about the sort of material they're interested in.