Okay, I have to disagree, strongly, with the general review. These books are terrible.
I read these when they first came out, and even then I recognized just how terrible they are: the SF is a thin skin around an unconvincing romance plot. The economics Wren describes are "Throw it across the room with great force" levels of stupid. And the torture porn in the third volume is simply revolting.
If you want something like the Phoenix saga only, you know, convincing, consider one of Scott Westerfeld's pre-YA novels, like Evolution's Darling or Killing of Worlds.