Thanks for that link - seems a bit bizarre to me, now that I've read throught it.

If I understand it correctly, you can buy the new non-pre-paid satchels to use via C&S, then pay the difference per parcel to ultimately pay the same amount as a pre-paid satchel. (That is, if the new 500gm satchels are 20c each, the postage for them will be $8.05). 

Alternatively, use your own packaging, and pay $7.20 for postage - most people can get generic satchels for less than $1.05 each, so I'm not sure I see the advantage of the new satchels at all - at least, not for anyone who doesn't qualify for the 10% off rates.