When Universal Containers uses the Draft with Einstein feature in Sales Cloud to create a personalized email, the predefined adjustment to Make Less Formal is the correct option to revise the draft with a more casual tone. This option adjusts the wording of the draft to sound less formal, making the communication more approachable while still maintaining professionalism.

Enhance Friendliness would make the tone more positive, but not necessarily more casual.

Optimize for Clarity focuses on making the draft clearer but doesn't adjust the tone.

For more details, see Salesforce documentation on Einstein-generated email drafts and tone adjustments.