I think your zone card is fine if your journeys are regular. However mine are not, and if you don't have Oyster the fares on bus and tube are ridiculous, presumably deliberately so to encourage use of the card.

I have mainly used my card on buses up to now where it is a simple matter of checking in on the way on. I guess checking out should theoretically be as simple, but quite often I seem to have machines that can't read the card.

As to checking the balance, you can see a trip report on line for the last 8 weeks if you register. I think it also shows the current balnce as you check in each time but my eyesight isn't that good!

I wish it had been available on the trains when I used to travel two or three times a week and couldn't justify a season ticket. To be honest I would trade the occasional error for not having to queue to buy a ticket.