I don't know - I am not a CSST expert, and the NEC does not cover CSST. That is my whole point. I get tired of gas men telling me I have to run a bond to their piping, and none of them ever have same requirements as to what they want done either. My opinion is it is their piping, I have met NEC requirements in most cases by having an equipment ground run to the gas appliance(s). If they want to install an inferior piping system that needs additional grounding methods then they better learn how to install their piping system to its specifications. In more recent code I have been required to install this intersystem bonding device, and as far as I am concerned they have one of those other systems that this is intended for - and it keeps them out of the electrical panels.
A CSST "expert" is a rare entity. The reason for requiring the "bonding" of the material by an electrical contractor, is because it falls under the purview of electrical engineering and the sizing of the conductor is determined from NEC 250.122. Bonding of regular schedule 40 or 80 is required under 250.104(B) but for a different reason. The same principle but different reason.
250.104(B) is bonding of the piping that may possibly become energized by an electrical circuit.
The bonding of the CSST is required for lightning protection.
There are three technical committees from NFPA 54,70, and 780 along with independent third party testing that are working to create safe design and installation procedures.
If CSST is used on a job, charge to install the bonding the same as you would do for running a circuit to a hot water heater or air conditioner.