I'm getting started with Flex and initially installed the Adobe environment (**Flex** Builder 3) and later found out that they're starting to call it **Flash** Builder 4. 

Anyway since I'm very new to this technology and I have to leave Flex Builder 3 anyway, I'm trying to find out if there are any advantages to developing with Adobe's Flash Builder 4 (adobe's commercial IDE) vs. Eclipse (which Adobe seems to also heavily support, they make and support a special plugin for it). 

My main language is PHP so my end goal is to integrate Flex with PHP. It sounds like Adobe did a decent job with integration in the Flash Builder 4 release (you can choose a language and choose data services options, etc. which should make that integration smoother), but is that integration only available through their commercial Flash Builder 4 or is it also available through the plugin they release for Eclipse? I'm trying to get some advice from those who used the technology so I can make up my mind whether there's a lot of advantage using Adobe's commercial IDE vs. the very robust open source Eclipse IDE. Other aspects I may not have considered are also welcome. 

Note: I use php without a framework, and I keep also hearing Zend from Adobe themselves, which is kind of confusing too. I guess they're using part of the zend for remoting. Does anyone know how zend will affect my flex development environment?