Use MyISAM on Replication Slave for read intensive apps

I have a master DB using InnoDB, and three slaves currently also
running InnoDB for a read intensive apps.

We don't use full text search, so there is no force for us to use
MyISAM. But we know that MyISAM table level locking is extremely fast,
as our master is already using InnoDB (i.e. free of locking issue),
will it be a good choice if we convert our slaves to use MyISAM?

(we might add more servers as slaves in the future)

Thanks.