Is Thorpe Park fast track worth getting during weekdays school time?

Me and some mates are going to Thorpe park on the 4th of July. We've checked that schools are open that day and as it is a Monday we guess most people will be working so it will be much less busy than normal. Having foolishly gone during Summer Holiday times and weekends in the past we have always used Fast Track to skip the queues. Is it worth using during the term time week day or just a waste of money? How busy can we expect it to be?