I bought the bright orange ZTE Open C fxos phone to try it out.
Haven't done much more with it that travel around with it, mostly using it as a primary phone for calls. The battery life is insane on that one - I went about 4-5 days without charging it when I was traveling (barely any calls, mostly standby).
The good part was the HERE maps downloaded onto its SDCARD and I could use at least some of the GPS functionality when it is offline.
However for the same amount of money I could easily buy a Micromax or Karbonn phone which would have 2 killer apps to use - PayTM and Ola Cabs.
To be fair, most Android devices and iPhone would achieve similar battery life if you're not actually using the phone.
Apple claims to get 10 days of standby out of an iPhone. I would imagine with 'barely any calls' or using the device you would get somewhere between 5 to 10 days. 5 days doesn't really sound that impressive.
I have a work iPhone that I barely use (since I prefer Android personally), and it usually lasts 4-5 days.
Since Mozilla stopped developing and selling Firefox OS smartphones a while back, you don't get to see those for sale on major retailers.
I still own (and use) one. Agree that it's a bit of a pain. But if you need a phone for making/receiving calls and test messages, it's reasonably good (especially for the price). Not bad if you get a phone for $30 and you're still using it for almost 2 years.
But, the perhaps bigger issue with Indian phones is the locking down of firmware. Spreadtrum (the SoC in the phone that you're mentioning) has all sources (device + kernel + vendor trees included) for compiling FFOS for the "tarako" board (upon which 3 of the first $35 FFOS smartphones sold in India were based).
However, I'm not sure up to what extent you can modify their firmware. Github user abgoyal (forgot his HN username) had a fair amount of success acquiring the kernel sources for his $35 FFOS device from the vendor ( https://github.com/abgoyal/zen_u105_kernel ), but iirc he had issues with those sources too.
Now, if I want to buy that particular device (since its open) to have a cheap $35 _thing_ to break, unfortunately I can't, since they stopped production.
Thats me. That repo has fully funtional source for the Zen variant of the phone. The Spreadtrum sources are enough to get started on other variants, but you will have to hack support for the dispay and possibly the touch panel.
It was a very interesting exercise getting stock debian onto these babies. I have been hoping to write it up for a while now, but never got around to it.
https://lwn.net/Articles/680109/ is the most promising.