There are several solid consumer-facing phones in this price range. This is not a consumer-facing phone. It contains a very specific hardware profile that isn't matched by those consumer-facing phones. This is a "reference phone" containing "reference hardware". In addition, it's the phone that Mozilla is standardizing Firefox OS development on, so it will have lots of other Mozillians using it which is important to many in the Firefox OS development ecosystem.
This phone is designed to be a superset of the hardware of other FirefoxOS phones. In theory, any hardware feature on another phone will also be found on this phone. Additionally, this phone has features like the ability to artificially limit the amount of ram it has, to test other device profiles.
> how is this better than using the emulator then?
Well, the emulator is not quite as comfortable for testing, say, calls, or SMS, or gyroscope, etc.
> also, how is this any different than the last 4 times this was done?
I am not aware of 4 times. However, it is true that Preview/Early Access Developer Phones have been released in the past. This one is not a Preview. IIUC, this one is considered stable.
Notice in its feature it has reduced system RAM controllable by software so you can mock up reduced performance phones... like those that will be sold in emerging markets.
