BTW, you might not have noticed, but three of the five nominees for the Hugo novels this year were published by Orbit Books, in London. The ideology that marked them was "Hey, we don't want to lose book sales by giving away free copies in the voting packet, let's just do excerpts!" Correia's trilogy was published by Baen, and the Wheel Of Time series, 15-or-so volumes, which got nominated as a single work, was published by Tor, both of whom included the entire sets, which I liked much better. (In Correia's case, Volume 3 was the new work that was actually nominated, but including the first two made it make a lot more sense.)
Excerpts didn't do the job for me. It's not just that I'm grumpy because I'm cheap and consider getting the nominated novels part of what makes it worth paying for the voting membership*, but it also affected how well I could judge the work before voting. For Stross's book, which I was planning to buy anyway, it was enough; for Mira Grant's, it probably was (though so far it doesn't look like as strong a work as the Feed series.) But I know both of their work and have read most of their novels, so I've got some idea of where they might be going; Ancillary Justice was Leckie's debut novel, and while the excerpt was enough to get some flavor of her writing skill, and see some of the things she did in the first few chapters, it's a bit of a slow start, I didn't get sucked into it, and also I can't yet tell whether the main character is just an interesting and complex post-human or a totally creepy slave-taker.
* The package includes the Hugo novels or excerpts, the Campbell-nominated works (mostly novels), all the shorter works, most of the graphical material, a lot of short stories in this year's short-form editor award, a really amazing related-works section (this was a good year for that), all for the cost of a supporting membership for the upcoming Worldcon, which is usually about $40. You get to nominate for the Hugos if you bought it in time, and you get to vote on the winners.