Some other differences between Octopus and Yikatong:

-- Getting a refund on Yikatong cards is difficult, since there are only a few refund centres; just assume you'll be keeping the card as a souvenir.

-- Not relatively easy to add value to an Yikatong card; learn to use the machines in the Metro stations.

-- On some Beijing buses -- those with distance-based fares -- you swipe both getting on and getting off the bus.

-- If your father is 65 or older, he should get the Elder Octopus, on which most public transport is charged at just HK$2.

I also had a difficult time buying an Yikatong card at Beijing West; turns out they're sold at a very obscure hole-in-the-wall (literally) at the far eastern edge of the bus stand.