Whether you use a mantra or kong-ans is not important. What matters is how you keep just-now mind from moment to moment. If you understand this, you can always keep enough-mind.
There is one important point about mantra practice you must understand. With mantra, getting one mind and samadhi are very easy. But you cannot find your True Way if you are attached to mantra. Mantra alone has no direction. However, always asking yourself, “Who is doing the mantra?” means having a direction. Having a direction means keeping a question and letting your cognition become clear so you can perceive your correct situation.
So only mantra is one mind, but if you keep the great question and mantra, that is clear mind.
Only-go -straight don’t-know mind is clear like space. There is no subject, no object, no inside, no outside. When you are doing something, you must do it. aIf you are not thinking, that is correct mantra and correct don’t know mind. What does the cat say? What does the dog say? You already understand.
-Zen Master Seung Sahn “Only Don’t Know, Pg133”