Is the use of Trackit mandatory for certified companies? 

As a certified company, the scope certificate data which you submit to certification body will be reported to Trackit. For transactions, there are two options: 

dTrackit: If you choose to continue using transaction certificates, then the transaction certificate data that you submit to certification body, will be reported to dTrackit. There is no need to directly interact with dTrackit.  

eTrackit: Alternatively, you may opt to upload your scope certificates, register sites, and carry out eTransactions in eTrackit. Commercial use of eTrackit for RCS and GRS is now live. See eTrackit Brand Toolkit and eTrackit Quick Guide for Brands.