A few things to keep in mind:
- Any already existing projects will only open in the current Flash builder.
- Any new projects, once created in the new builder, will only open in the new builder
- It is still a beta (early beta) so some features will not work or not yet implemented (from the Flash builder)
When creating a new app, click More create options:
Check Open in new (beta) app builder option:
and this is thew welcome screen in the new builder:
The new visual designer: