I did the Level One course back in July and struck gold: my instructors were Charlie Boorman and Simon Pavey no less. Charlie is training to be a BMW off road instructor, and me any my mate just happened to be placed in the team which had the winner of Bike Magazine's competition for a course with CB. What a stroke of luck !
We rode down to Abercraf from Manchester and stayed at the Abercrave Inn (book well in advance). I rode the 1200 and my mate the 650. Course was excellent, but make sure you have:
Proper Off Road boots - you can hire them there, so no probs.
Knee pads - they have them there too - free of charge to borrow
Organisation was A+, my bike was pretty rough despite having only 3000 mls on the clock, but after 2 days riding round in max 3rd gear, was obvious to see why. Was a godsend to get back on my own bike after a day in the hills.
Took some time getting used to the off-road brake and clutch position (levers angled down, makes it a lot easier when standing up) and getting the confidence in just using 2 fingers for brake and clutch control, but after an hour was second nature.
After 2 days, you will feel it in the shoulders and forearms - but worth the pain. The included meal at the Abercrave Inn was excellent, but was relieved to be sleeping there after a few pints.
Book it, do it and enjoy !
Martin