It seems a great deal - means that if you don't travel in the AM peak,
daily capping will be slightly less (IIRC) than buying a weekly Z12
travelcard. *With the proviso of course that it's valid on almost no
NR services south of the river. *The recent extensions to oyster
validity seem to have made the system even more biased towards North
London - as the map athttp://www.tfl.gov.uk/assets/downloads/tickets/oyster-PAYG-08-01-02.pdf
shows.

As a resident of one of the five (or is it six now?) famously Tubeless
boroughs, I'd love to agree with you. But surely it's because more NR
stations north of the river already have some sort of Oyster-handling
equipment (and in some cases, like Blackhorse Rd or Kentish Town, are
more Tube stations than NR stations anyway), so it's easier for them
to plug the gaps?