Tekpower TP3005T Variable Linear DC Power Supply, 0-30V @ 0-5A with Alligator Test Leads

What are advantages of a linear supply? Are there specific uses that it is ideal for? ( As ompared to a switching supply with greater efficiency)

How do you enable Constant Current mode? The instructions say to press and hold the current button, but all that does is enable/disable lock mode.

If this is a dc psu what s the ground for? does it provide an ac supply as well? switchable between ac an dc?

do the leads have diodes, or can charging a battery backfeed power into the unit?