Nearly 3 weeks on and I'm still using the ZTE Open C as my primary device. I continue to find Firefox OS charmingly simple and surprisingly smooth. So far I've only had one minor hiccup when my early morning alarm call went off at lunch time o_0. A reboot seemed to fix that and I haven't had a problem since.

At the risk of sounding a little paranoid I feel quite liberated that there's no Google crapware preinstalled to monitor, track and profile me.

I think Firefox OS is plenty good enough to grace better hardware than it's currently getting.