Thanks for getting back, @enrico.
I can help provide additional information about the difference between the two items.
A service item will include charges for professional fees that your firm buys or sells. If you're creating a service item used in purchases, you record your vendor's unit price as rate and choose an expense for the account. If it's a service item you sell, you record your typical selling price as the rate and choose an income account.
The non-inventory item is a material bought and/or sold, but not tracked as inventory part. QuickBooks won't track the quantity on hand nor the value of these items.
Also, a service item is available for timesheet use which is not available in non-inventory.
Keep me posted if you have other questions about using the service item. I'm here to help however I can. Have a great weekend.