Having auditioned the Samsung ARM Chromebook (very similar hardware, the HP uses the same Exynos SoC) as a dev notebook, I have to say pressing Ctrl-D every time you boot gets pretty old pretty fast. This is exacerbated by poor power management. Also, I wouldn't make too many assumptions about how well things might work - setting up the 3G data was a pain and the trackpad was super-fussy running native Ubuntu/Chrubuntu.
Most devs that use Chromebooks for development either end up using the Crouton chroot or running everything remote, but I've found both options less than satisfying and missing some basic affordances, like a working clipboards, launchers, or a modern terminal app. It'll get you there, but it won't be pleasant.
It looks like the HP's screen is better (the Samsung's TN is pretty terrible), but I'm still disappointed the these low-power ARM laptops have such crappy batteries/battery-life.
As a developer, your best bet for an ultraportable is probably still a MBA on OSX or something like the Developer Edition XPS for Linux. These are about $1000 more expensive, but provide a whole different level end-user experience.