What is Flash Builder 4.6 Premium?

Adobe® Flash® Builder® 4.6 software is a development environment for building applications using the open-source Flex framework and the ActionScript® language. Flash Builder Premium includes professional testing tools such as profilers, network monitoring, and unit testing support.
Flash Builder 4.6 is based on Eclipse™ and offers both a visual design environment for designing application user interfaces and a full-featured development environment for the MXML and ActionScript languages.
Is Flash Builder 4.6 the latest version of Flash Builder?
No.  Flash Builder 4.6 was first released in November of 2010 as a free update to Flash Builder 4.5.  Adobe is continuing to make Flash Builder 4.6 available for purchase in order to support users who are maintaining development environments for Adobe Flex 4.6, as well as those who rely on the visual design facilities available in Flash Builder 4.6.
Does Flash Builder 4.6 support Design View?
Yes, Flash Builder 4.6 includes a full visual design facility for creating Flex-based applications.  Flash Builder 4.6 also supports visual Data-Centric Development for connecting front-end application components with data sources.
Is Apache Flex supported by Flash Builder 4.6?
Flash Builder 4.6 was released before the creation of Apache Flex, and was only designed to work with specific versions of Flex.  Users of Apache Flex should consider using Flash Builder 4.7, which has full support for Apache Flex.
Does Flash Builder 4.6 support the latest versions of Adobe Flash Player® and Adobe AIR®?
Flash Builder 4.6 shipped with support for Flash Player 11.1 and AIR 3.1 via the Adobe Flex 4.6 SDK.  Flash Builder 4.6 has not been tested with newer versions of the Flash runtimes.
I already have a license for Flash Builder 4.5. Do I need to purchase a license for Flash Builder 4.6?
No, Flash Builder 4.6 is a free update for Flash Builder 4.5 users.  Download the Flash Builder 4.6 trial from http://www.adobe.com/support/flex/downloads_updaters.html and use your Flash Builder 4.5 product key to activate.