I would advise against the Geeksphones unless you're looking to use them as purely test devices. They were intended as developer phones, not for consumers. They also have some really frustrating issues:
* Both devices still run (AFAIK) FXOS 1.1, which is really very out-of-date. You can flash them with updated versions from Mozilla, but you have to do it yourself. OTA updates will probably not happen. New devices still ship with old versions of FXOS.
* The Peak has a very large screen, which was not something that was fully supported when it first shipped. Some of this has been sorted out after updates, but I occasionally still see people frustrated by poorly scaled interfaces.
* The Peak suffers from a bulging battery issue. The manufacturer has assured everyone that the issue is within tolerances, but it made me uneasy. The battery bulges enough that the back cover of the phone does not sit properly.
* Both devices suffer from charging issues. If you completely drain the batteries, it becomes nearly impossible to charge them. As soon as you plug the device in, it tries to boot, which saps whatever charge it just received. The device shuts itself off, then tries to boot again as soon as it has the tiniest amount of charge. If this happens, your device is basically useless.
* Maybe out of the box, but geeksphone does make really nice install scripts and has available every version of FxOS available on their site. [0] Maybe directions about turning on remote debugging first on the device would help, but I'd say they've made it pretty easy. A README would be nice, but they even ship OS specific builds of adb and fastboot in the zips.
* Launching the first 3 devices with the screen resolution of 320x480 and not supporting others in the simulator certainly contribute authors to only testing on one resolution. I myself was guilty with the calculator. But I'm not sure that this is a reason not to get the phone. Maybe you're referring to bugs in some CSS calculations? Do you have any bug numbers off the top of your head?
* Yes, I raised an emergency warning when I saw this, but Geeksphone themselves said that was a safety precaution and was expected. It was due to the battery over heating. I only saw this occur on a peak that we were stress testing WebRTC builds on.
* No. It will do stupid reboot cycles when the battery is basically empty like you said, but that doesn't make the device useless. Letting it sit and charge does the trick.
* Both devices still run (AFAIK) FXOS 1.1, which is really very out-of-date. You can flash them with updated versions from Mozilla, but you have to do it yourself. OTA updates will probably not happen. New devices still ship with old versions of FXOS.
* The Peak has a very large screen, which was not something that was fully supported when it first shipped. Some of this has been sorted out after updates, but I occasionally still see people frustrated by poorly scaled interfaces.
* The Peak suffers from a bulging battery issue. The manufacturer has assured everyone that the issue is within tolerances, but it made me uneasy. The battery bulges enough that the back cover of the phone does not sit properly.
* Both devices suffer from charging issues. If you completely drain the batteries, it becomes nearly impossible to charge them. As soon as you plug the device in, it tries to boot, which saps whatever charge it just received. The device shuts itself off, then tries to boot again as soon as it has the tiniest amount of charge. If this happens, your device is basically useless.