Direct from the cedar council on the installation of cedar shingles is, use no field underlayment. This is on a new home in the south east US
Mount it straight to the plywood with a run of paper over the eaves and one up the rake.
I looked at that breather product as well, before I contacted the cedar representatives, as it seemed to make sense to keep some kind of airflow underneath the wood. The install directions said no.
I would imagine there are very specific nailing patterns for higher wind zones, if that is in fact an acceptable roof covering at all in those areas.