My HTC Hero (which is totally obsolete by now - you can't upgrade Android phones once the manufacturer released other phones and doesn't care anymore) is only fluid on the home screen. Everything else (even the Play store!) is slow and laggy. I can't play most games and can't install most apps on the Hero (armv6 means no Firefox, no Telegram, no 'anything using jni').
So I strongly disagree: the Keon is good enough, and the first Android phones were NOT better (you seem spoiled, high-end user! Just because it's not as fast as $400 phones does not mean it can't be interesting).
HTML5 based os need a lot of processing power,webos already proved it in the past. That's why firefox os will fail,it's not designed for lowend devices.
You seem like you can't conceive that html apps on a FirefoxOS phone can be just as fast as any good app on another phone.
If you tried Cordova/Phonegap on Android and didn't find the performance adequate, if you tried a web view on iOS and didn't find the performance adequate, just don't take the shortcut of believing that you would get the same inadequate performance on Firefox OS. The whole stack is different.
HTML5 based os need a lot of processing power,webos already proved it in the past. WebOS and its fate proves nothing regarding the performance of mozilla's OS.
That's why firefox os will fail,it's not designed for lowend devices. It IS designed for lowend devices. My Keon boots more than 3 times faster than my HTC Hero. In its early days, B2G was even booting in 10 seconds (flat). You just didn't see it with your own eyes.
I suggest you revise your 'pure crap' opinion when you actually see the OS running in front of you.
If this was a troll (feature phones? are you kidding me? We're talking about a phone that can really browse the web, here), I don't know what to say. Otherwise, you're just full of FUD.
Disclaimer: I have only used the Keon. I don't have any experience with the ZTE or another one, but I'm still pretty confident they're not 'pure crap and a total waste of money'.
If it's not your main device - try nightly!