Without the advantages of lots of sanzen I think most people are left with floundering around with their sussokan. I am not sure people are really moving along from their Mu breath to inquiring mind. The Roshi has written in beginning instructions to ask who am I? or what is this?

If the way we use MU is too indulgent, then we can not experience the truth with our whole mind and body and it becomes a conceptual way of going about it. Then, no matter what tool or words we use, it will turn out to be conceptual. We need to use Mu in a way that our mind and body can melt into it. For that it needs taughtness of energy in everything we do. If we still get moved around by the outside world, we cannot reach that inner fullness. Conceptual play is of no meaning whatsoever.