A membership site needs to be able to grant access to posts belonging to a membership, and a user can get multiple memberships, which actually creates the need to be able to apply multiple roles to a user.
This is not possible in Access. But is this on the TODO list?
Until then I will have to continue to use a dedicated membership plugin.
But in order to be able to build a real membership site, you need to be able to apply a "right" to a user upon purchase of a specific product.
And if you use Access you can only control access by linking a user role to a content group. But this is too limited to really being able to use Access for a membership site.
Because a user can purchase product a, b and c.
Each product grants him rights to a specific membership which in access terminology is a user role.
But since multiple user roles are not possible in Access, you can't have a granulated access / membership configuration with Toolset Access.
So really it is a feature request in order to be able to build membership sites where a user can have multiple memberships.