What Apps can be on SD Card??

[shiflerg]

I have gone to app manager and chosen a few apps at random. I see that the "move to sd" is greyed out. Is this because I have do not have a SD card. If I add a SD card, can I move any app to that card? What are the restrictions on moving apps to the sd card??

A second question is about the SanDisk uSD cards and the Galaxy S4. I have read about major problems with this. Is there any recommendations on a uSD card for my Galaxy S4?