The beba cards are free of charge and are available from beba agents in certain locations. Google is using Top Image - the same company that markets M-PESA- to market the beba cards. You need a gmail account to activate and load your card with money from a beba agent.
I obtained a beba card and loaded it with money from an agent at Kencom and I used it to pay for my bus fare immediately.The conductor taps the card on a NFC enabled cellphone and you immediately get an sms receipt from the short code 2729 showing you the amount you have used, the bus company that you are using and the balance on your beba card.
Beba's main selling proposition is to help people save money. The bus conductors and matatu touts have been known to hike up bus fares the moment it starts raining or when there is traffic. This is the problem that beba is solving for commuters.
You can view all the transactions you have made from the beba website - that is, the date, amount and location where you loaded the beba card with money, the bus company you used, the amount you paid and the final destination where you alighted from the bus. You can easily claim for a refund in a case where a conductor over charges you because all the evidence is there in your account.
The conductor of the Citi Hoppa bus I was traveling in was visibly not happy when I handed him the beba card. The conductors sometimes charge you but they do not give you a receipt meaning they pocket that money. That also means that they do not have any incentive whatsoever to accept the beba cards from commuters.
Google have got themselves a niche and they are solving a real problem. It will be interesting to see how they will scale the beba service, especially so in the notorious and chaotic matatu industry.