AFAICT the difference in the provided example is that it provides a custom message package in ROS 1 and ROS 2 format. This allows to test overlay workspaces out of the box with instructions on how to build them (namely running catkin_make on the ROS 1 version and ament build on the ROS 2 version). The rest of the difference are modifications to the bridge CMakeLists to find ROS1 message packages (applies only for users using pre-beta2).
@mch Would it be possible for you to test your example with ROS2 beta3 without all the CMake modifications and confirm that no code change is required to transfer custom messages through the bridge? I think it’s great to have quick start guides and would love to see a stripped down version with only what is required to make it work to avoid confusing users with unnecessary code changes.