Hi Rob,
I went and did my Balance training last January. Although I was certified in Combat, Pump and Attack, I was still freaking right out! Simply because it doesn't matter what training you've had previously, you're doing something completely new!
I went to a Balance class for about two months before training (hey, I teach x amount of permanent classes/week, I have limited times to attend other classes in their entireity).
Yes, they will go through the usual Les Mills thing - circle of instruction etc. I didn't find the Balance "challenge" too bad. It was hard, but I've been through a lot worse (thinking of Combat where the skin of my feet was coming off, and Attack where I shed bodyweight, in sweat, in the plyo circuit, then had to do the 'beep' test right at the end of the first day). I did have to hold poses for a freakishly long time compared to the other trainees, but the Master Trainer told me afterwards that it was because I was very strong (dammit!) and she could leave me there awhile whilst helping others.
I did find learning and cueing Balance very difficult (it's very different from Combat, and so much more depends on the instructors cueing), plus I had three days in a row (so not even a week to practise my final track, only one night). Whilst I enjoyed my training, it was stressful, and I never really 'relaxed' (but I am typeA when it comes to my teaching!).
Even though I'm actively teaching it now, it is a program I really have to work hard at (well, harder than the others), as there is just so much info (safety, technical, right cue/right time) that needs to come through in the class. It's not a 'soft' option for me, and has become my 'challenge' program. I always script every class, dot my "i's" and cross my "t's" when it comes to the safety and chorey side of things. I find it hard to learn as it's not always a 16/32 count choreography. I really have to listen to the music to find the 'changes' moving from one pose to another. But, the feeling of giving an excellant Balance class is second to none!
My advice is, this class is so different, it requires so much more of you as an instructor. Be prepared to work hard at it all the time, from the initial training, all the way through to your permanent class/es.