Even on a 4.9" screen, music shared and lti-window/mult-tasking features can be quite productive whether using them in portrait mode or landscape mode. On my 4.1.2 SGS3, Samsung Multi-window and Swapps Sliding App Drawer give me a lot of control of my apps and the tasks with which I'm concerned though more refinements are definitely needed.
Currently, I have only 21 out of 169 downloaded (and used) apps that support the Multi-window feature [refer to my reply in the Multi-window discussion for a list of tested apps]. That clearly shows some timidity at Samsung and a wait-and-see attitude within the Android development community.
Both Multi-window and Swapps are resident applications with sliding app drawers that can be turned on or off at user discretion. Both provide screen position options (left/right/top/bottom) and can be tapped closed (invisible) when not needed.
There's a lot that can be shared and discussed here; but, for now, I'll close with an invitation to all to reply with your comments and personal insights into the use of multi-window and multi-tasking applications on the SGS3i535. I have some screenshots of how both applications look on my S3, but cannot find a link for attaching them here. Maybe Ann_154 can email me and I will attach them in my reply posting.