EZ-Flash USA Forum

whats the difference between this site and http://forum.ezflash.cn/??

EZFlash forums. There has always been a Chinese language forum of one sort or another but over the years (I have only seen two) but as far as English forums

There was originally one on ezflash.com.cn I think it was several years ago (a while before the launch of the EZ3), I forget what software was used for these.
This was replaced by another a couple of months before the EZ3 hit (using vbulletin as I recall). Most people that remember the "old" .cn forums will remember this one.
It was however very slow so sosuke founded this one as an unofficial one. It had a little following at first but slowly took off.
The "old" forums died under a DDOS attack and these became the forums linked from the ezflash website. They did appear once on another domain but enough of that.
The new .cn forums you linked to were founded during the site relaunch a few months back. A few people go there but this is still the main place.