My DS also went for a mock exam- well he didnt particularly score well, but i found out at later stage that kids who use the website where the mock exam originated really do well in that mocks. And the style of questioning is different to ABGS. There were only about 50 kids- and the feedback was not very useful either.
Even though DS aced his alty exam .......i think what prepared him was the mock exams i had for him at home. 6 weeks prior to exams, every weekend we had a mock exam. Timing and practice are the key words for 11 plus exams. The more practice you have, the better and confident one will become. During mock exams- we planned for all types of scenario- noises, toilet trips, pencil dropping, strict time guidelines- and what to do when if you find yourself running out of time.
I found the mock exam we paid for, quite a fortune, was not really necessary- but i can only say that on hindsight. If i have another child who is going to go thru 11 plus- i dont think i will pay for a mock exam- i will just conduct one on my own.