A single Customizer can be used for similar products that use the same set of inputs as defined in the Customizer.
For example, if you have a laser engraved leather mouse pad, the Customizer could have a color choice (brown leather, black leather, red leather), and a place for ten engraved characters of text, this would be a single Customizer. If you have photographs showing each unique combinations of options (e.g. black leather w/ Anderson text, and red leather w/ Williams text, etc.), those would be products under one Customizer.
If you have a similar item, but it uses different inputs to produce - one design uses 10 characters of text, but another uses a single letter as a monogram - then it would be best to create a different Customizer for each by duplicating a Customizer and cloning it. Why? If they were part of the same Customizer, a customer may want to create the monogram version but still have the ability to add 10 characters of text. That would create confusion for the customer and for you when it is time to produce the item.
If you have questions about this for your own products, please don’t hesitate to email Maker Support for guidance.