Go with a quality TDO and you'll be fine. I use Bookatrack almost exclusively as Johnny & co run a very tight ship that will give youna fair amount of leeway unless you're a complete idiot, and then they'll come down on you like a ton of bricks, and that works very well.
For the opposite reason I avoid Circuit Days like the plague, I've seen some atrocious driving that was let go because the driver was friends with the guy running the day. I've still got the video to prove it too...
A Walshy day is incredible fun, but not a patch on a proper track day.