Yes, the discs are very helpful. We also did a session with the instructor at the training company practising technique for the hazard test. Good luck!
I used the hgv theory test book and the discs.... but the hardest part for me was the hazard - as an experianced road user you see something deal with it and click too soon - i got done for inapporpriate mouse use ! but passed - got 100% on the theory though !
Have you got a smart phone? I downloaded an app and i have to say it was inexpensive and worth its weight! Could get tested all the time and work on the areas i was weakest!