Final answer:
To allow product specialists to see all cases for their product line, implement criteria-based sharing rules for each product line at Ursa Major Solar within their private sharing model.
Step-by-step explanation:
To set up a system where product specialists at Ursa Major Solar can see all cases involving their product line with a private sharing model, you would use criteria-based sharing rules for each product line. This approach allows you to automatically share records that meet certain criteria (such as involving a particular product line) with a group of users (the product specialists), without the need for manual intervention each time a case is created. A role hierarchy would not be as effective in this scenario, as it's based on the organisation's reporting structure rather than the product line specialty, and manual sharing or ownership-based rules would be inefficient and not dynamic.