I don't know the structure and the actual source of the data
However find my approach below
Once you connected the data use Custom spli to get the values in several fields/columns like this
Once done you'll get something like this
then copy the whole data and paste it in excel and delete the Product field
then you'll have only
Now connect this new source in tableau and select splited fields and use pivot option to get the values (Split 1-5) from columns to rows.
Once done you'll get this view. You can put data source filter to hide the null values.
Post hiding null you will have this data. Rename the Pivot Field Values to Products
Now go to worksheet and drag the fields like this
You can create a parameter with all the product values like this
Now use this parameter to create a calculated field to get the distinct count of Customers
Only problem with parameter is single selection. Let us know if any of these helps.
workbook attached for your reference.
Option 1 & 2_v10.2.twbx 13.5 KB