Being a pre-stage 2 applicant I can't say very much! I can say that I was the one who suggested the heronet games. One of which required a player to complete three simultaneous games of tetris.
I have also heard and read about SkyTest for NATS ATCO Screening.
It is designed to help applicants pass Stages 1 and 2 of the NATS screening process - Could be useful. Seems expensive on their website though.
Lastly, it might be obvious, but I suppose the games on the NATS website might be useful?
Cheers,
Phil