How to use a list in a list in report builder?
In my humble opinion, it depends on the complexity of the details view.

If I'm showing a sample list of values in each view then I'd rather use a List inside a List, inside a List.

For example:

[+] Customer Id + Customer Name
    [+] DeviCe Id + Device Name
        |------------|-----------------|
        | Job Id Job | Job Description |
        |------------|-----------------|
        |------------|-----------------|
        |------------|-----------------|


But, if the details view have a more complex structure, like graphics + tables or matrix, then I use a subreport.