What's the difference between a Apple Watch Hermes and a combination of a normal Apple Watch and Hermes strap?

Hi

There are no functional differences.

Apple Watch Hermès models include:

• Exclusive Hermès-branded watch faces, along with all of the standard watch faces under watchOS.

  Hermès watch faces cannot be installed on any other models of Apple Watch.

• An additional Sport Band, along with the leather Hermès band.

More information:

Apple Watch - Compare - Apple

Apple Watch Hermès - Apple