Which is easier to manage for the user?
In this case It's needed to have a lot o serial number for purchase items, allowing searching by this concept in all the modules.
I can't see the difference between using unitary lot and serial number (Service is not implemented)
Please could anybody give me a piece of advice?
Thanks

Lot by Unit is actually making an item Serial Number Control. Each Item is required to have a Lot/Serial Number. Lot Control means you can have the Same Lot Number assigned to multiple Units.