Futaba 3pm question

I just bought one of these radio and have been trying to figure out the same stuff.
I don't really know the diference between hrs and ppm but, You can switch between the two modes.

In ppm mode you set the fail safe each time you turn on the Tx by pushing the button on the back of the Tx. It only effects the the throttle (Ch 2) and has no effect on steering. I don't really like that you can't permanently set the fail safe.

When it's in HRS mode you set it through the menu. Only problem is that some of the brushless ESC won't work with HRS.