Yup 
Chanting 'Buddho' is a very common
practise and recommended by the great Theravadin masters... Not
only Ajahn Mun, the meditation masters I've read especially the
Thai ones have always recommended this practised, including Ajahn
Maha Boowa and Ajahn Chah, and many others.
Here is an excerpt from
http://www.amaravati.org/abmnew/index.php/teachingsofajahnchah/article/387/:
Clarity of Insight1
Meditate reciting Buddho, Buddho 2 until it penetrates deep into
the heart of your consciousness (citta). The word ''Buddho''
represents the awareness and wisdom of the Buddha. In practice, you
must depend on this word more than anything else. The awareness it
brings will lead you to understand the truth about your own mind.
It's a true refuge, which means that there is both mindfulness and
insight present.
Wild animals can have awareness of a sort. They have mindfulness as
they stalk their prey and prepare to attack. Even the predator
needs firm mindfulness to keep hold of the captured prey however
defiantly it struggles to escape death. That is one kind of
mindfulness. For this reason you must be able to distinguish
between different kinds of mindfulness. The Buddha taught to
meditate reciting ''Buddho'' as a way to apply the mind. When you
consciously apply the mind to an object, it wakes up. The awareness
wakes it up. Once this knowing has arisen through meditation, you
can see the mind clearly. As long as the mind remains without the
awareness of ''Buddho'', even if there is ordinary worldly
mindfulness present, it is as if unawakened and without insight. It
will not lead you to what is truly beneficial.
Sati or mindfulness depends on the presence of ''Buddho'' - the
knowing. It must be a clear knowing, which leads to the mind
becoming brighter and more radiant. The illuminating effect that
this clear knowing has on the mind is similar to the brightening of
a light in a darkened room. As long as the room is pitch black, any
objects placed inside remain difficult to distinguish or else
completely obscured from view because of the lack of light. But as
you begin intensifying the brightness of the light inside, it will
penetrate throughout the whole room, enabling you to see more
clearly from moment to moment, thus allowing you to know more and
more the details of any object inside there.
You could also compare training the mind with teaching a child. It
would be impossible to force a child, who still hadn't learnt to
speak, to accumulate knowledge at an unnaturally fast rate that was
beyond its capability. You couldn't get too tough with it or try
teaching it more language than it could take in at any one time,
because the child would simply be unable to hold its attention on
what you were saying for long enough.
Your mind is similar. Sometimes it's appropriate to give yourself
some praise and encouragement; sometimes it's more appropriate to
be critical. It's like the child: if you scold it too often and are
too intense in the way you deal with it, the child won't progress
in the right way, even though it might be determined to do well. If
you force it too much, the child will be adversely affected,
because it still lacks knowledge and experience and as a result
will naturally lose track of the right way to go. If you do that
with your own mind, it isn't sammā patipadā or the way of practice
that leads to enlightenment. Patipadā or practice refers to the
training and guidance of body, speech and mind. Here I am
specifically referring to the training of the mind.
The Buddha taught that training the mind involves knowing how to
teach yourself and go against the grain of your desires. You have
to use different skilful means to teach your mind because it
constantly gets caught into moods of depression and elation. This
is the nature of the unenlightened mind - it's just like a child.
The parents of a child who hasn't learnt to speak are in a position
to teach it because they know how to speak and their knowledge of
the language is greater. The parents are constantly in a position
to see where their child is lacking in its understanding, because
they know more. Training the mind is like this. When you have the
awareness of ''Buddho'', the mind is wiser and has a more refined
level of knowing than normal. This awareness allows you to see the
conditions of the mind and to see the mind itself; you can see the
state of mind in the midst of all phenomena. This being so, you are
naturally able to employ skilful techniques for training the mind.
Whether you are caught into doubt or any other of the defilements,
you see it as a mental phenomenon that arises in the mind and must
be investigated and dealt with in the mind.
That awareness which we call ''Buddho'' is like the parents of the
child. The parents are the child's teachers in charge of its
training, so it's quite natural that whenever they allow it to
wander freely, simultaneously they must keep one eye on it, aware
of what it's doing and where it's running or crawling to...
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