One important point that I don't see anywhere on the website is if to use this service do I need to add a GDPR banner? Does it use personal user data (like an identifiable number for each user) ?

Because if it does, I need to add a GDPR banner and opt-in mechanism, which I don't want. It is possible to do funnel analytics without using PII, and I'd like to know if Volument allows that (without their Tracking conversions feature obviously).