External Tables and UC Managed Tables are similar from the perspective of Delta's properties.
So, Time Travel and ACID properties are identical.
It comes down to 2 high-level differences.
1.
UC External: You decide the exact path for the table at table creation time.
UC Managed: You set up a Catalog and/or Schema Location, and Databricks decides the actual table path using a TableID in the path within that catalog/schema location path. (It's still your storage such as S3/ADLS/GCS)
2.
Databricks will "maintain" the UC Managed Table for you with features such as Predictive Optimization, Automatic Cluster Key Selection (for Liquid Clustered tables), Automatic Statistics using background serverless compute.
Note: You can do all of this yourself even on External tables but we'd like to take this burden off you, so you can focus on more important tasks.
From a performance perspective, assuming you did all the 'management' activities mentioned above, it will be the same. But you need to remember to do it, while with UC Managed Tables you will not need to.
