I agree with Rex. I personally did have one session. Having never flown a large 4 engine aircraft before, to then go in and fly a fairly in depth sim assessment, to at least have some idea as to where the instruments etc are was invaluable. It didn't make me outstanding on the day, but it did allow me to free up some capacity to concentrate on making sensible decisions, and show some CRM with my sim partner, which is what they are actually looking for.
The best advice I was given was, make sure your sim partner looks good, and you'll pass.
The BA assessments are mostly about the prep, and independently putting the work in. I prepped for day one, I spent a month doing practice interviews and thinking through every question I could find for day two, so what would have been the point in going to day 3 completely cold.
Having said all this, I think paying for a 10/12 hour course is a bit over kill, and really not necessary.
Best of Luck!