I've seen a lot of plans from CST.
You need to ask the advisor,
1) What is the cancellation policy?
2) What type of fee or administrative charge the plan is having?
According to my research, you need to pay some administrative charge for each unit you buy. The charge is pretty much the 95% of the unit you buy. For example, $100/unit and the charge is $95/unit. If you cancel or stop paying into the plan, your administrative charge will not be refundable. But if you keep paying until money in the plan is used to pay the tuition, those charges will be refund to you.