The BIT IS conditioners use sacrificial surge protection. They are $3 pieces that can be field replaced.
The BIT conditioners that are not IS use moving mode surge protection.
My confusion came from the Bryston website where the BIT 15 page says moving mode surge protection but when you open the brochure you discover there is a line of BIT conditioners that don't use moving mode surge protection.
The good news is the unit I purchased is a moving mode surge protection BIT 15 and not a sacrificial BIT IS 15.