In Contentful, you have content types to make up your fields and denote the type of data that will be included in items that will be created for it.
In the end of the day, the question on whether to create a single or multiple content models depends on how many specifications/fields will be shared among your items.
In the first case, if you were to have completely different specifications across your items, it would make sense to create separate content models, and subsequently create entries on top of each of them.
However, if you were to share many, or at least some fields, you could create a single content model (e.g.
product) and leave some fields empty, so that both
item2 belong to it.
Let me know if that makes sense or if you have any other questions