So Oyster is crap because you can't keep track of something as simple
as how much pre-pay you have on it?

It is a fault, yes. It is one that TfL would be able to solve quite
easily by obtaining a quantity of pocket validators and selling them
at ticket offices (or by mail order) to those who want them. I
believe they cost under a tenner a shot.

Will people please stop getting so defensive and assuming that
pointing out a limitation of Oyster is a statement that it is "crap",
as this is not the case.

This is not a limitation. The balance comes up on the screen of the
bus and on the tube gates - there is no way that you can't have a
rough idea of what you have.

Failing that the website has your balance on it. If you need constant
reminding of your balance get a nice smart phone or one with pocket
windows on it so you can log in anywhere.

Finally, I just can't see TfL encouraging any kind of Oyster reader
technology other than the ones they have on their premises/vehichles.
As the balance and ticket information is actually held on the card,
conceivably someone could attempt to add tickets/balance at home
using modified equipment. I'm sure there is fantastic security in place
to stop this but issuing take-away devices capable of "talking" to the
Oyster card that could be adapted, copied or modified is not a good
way to keep the system secure.