Both refer to the same UUID and you can calculate the numeric value yourself by decoding hex parts and multiplying. Those UUID values allow you to use UUIDs as primary keys on the database. Sorting and indexing can be more efficient.
Sadly FileMaker 17 does not introduce the UUID data type to store UUIDs efficient as 16 byte in binary representation instead of 40 characters of text for the number or 36 characters for hex representation. That would save space.
So please start using UUID numbers, which avoid people guessing your record IDs by counting up or down.
If you need those for FileMaker 16 or older, you can use our new plugin function UUID.Number. It returns you an UUID as number, same as with FileMaker 17.
We also got UUID.FromNumber and UUID.ToNumber functions to convert between hexadecimal and numeric representation.