Can non-owners install Mechanic?
Usually! A fresh install of Mechanic requires permission for reading online store content, like pages and blog posts. Any staff users who have access to that content in the Shopify admin will be able to install Mechanic.
The operative subject here is the granting of permissions to Mechanic. Staff users can only grant Mechanic the permissions that they themselves have been granted. If a staff user has full permissions for the Shopify store, for example, then they'd be able to install Mechanic and configure whatever tasks they like, granting Mechanic whatever permissions are necessary. Or, if a staff user only has access to the store's products, they will be able to install product-related tasks, but they won't be able to install customer-related tasks.
Note that this only applies to situations in which Mechanic needs new permissions. If another user has already installed a customer-related task, and has granted Mechanic those permissions, then any other user – even if they do not have customer permissions for the store – will be able to install additional customer-related tasks, because Mechanic will re-use its existing customer access.