You can book domestic JAL flights right up until departure if you use Avios. You can't do that with JAL miles. The taxes are trivial, too: in some cases, they are zero, and then you must add a donation to charity on the BA booking page for the transaction to go through. In other words, they are fantastic value, and this is even given the various discounted foreigner tickets that exist. International JAL redemptions are also worth looking into if you are in the Asia region for a reasonable amount of time.