For one thing, the link you provide doesn't contain that quote anywhere that I can see. Perhaps you intended to post a different link?
Secondly, I have been using a Firefox OS developer preview phone for several months (one less powerful than the ZTE, I believe), and the UI is extremely snappy. As all 1.0s it still has rough edges that I only hope will be softened by future upgrades, but I find the user experience generally pleasant.
Finally, you can certainly grab a refurbished iPhone if you prefer. iOS 6 is certainly visually nicer than Firefox OS 1.0. But the whole point of FirefoxOS is freedom from silos. One of the consequences is that the appstore will not simply drop support on you whenever Apple (or whoever owns your silo) decides that they want to force you into buying a new phone. Unless I'm mistaken, another of the consequences is that any application bought on FirefoxOS will still belong to you if decide to move to an Android phone or to your Windows/MacOS/Linux personal computer (sorry, no iPhone support, Apple wouldn't want that kind of thing to happen). Oh, and of course, with a Firefox OS phone, you can just write and deploy your own apps without having to ask anybody's permission. I wrote a (small) game during a conference and released it a few days later, before the Marketplace was even open. If visual effects are more important to you than this kind of freedom, yes, by all means, go ahead and buy a refurbished iPhone.
Caveat: I'm a Mozillian.