Hello Dave,
are you launching the roadmap from this page in Service Marketplace? I have just tested this link and it opens the right roadmap view - e.g. the Simplified RDS Experience.
As for the differences between the RDS and Simplified RDS Experience - the later is based on the Assemble-to-Order model and thus closer in its outline to ASAP with Agile elements than to RDS at least on the lifecycle phase level.
Best Regards, Jan