The A2 disk is now available at the same pricing as the AS disk. It has the same format with all the core experiments, some additional practical work and the A-Z index.
There is a special introductory offer for additional disks - £60 for a pack of ten. This offer also applies to the AS disk and is available until the end of 2009.
If you find the AS disk useful, then the A2 disk should be equally helpful. However, if you are not sure it is available on the usual 30 day free trial. You can make an online order here.