Locale X is a major new version. For all of the new features in Locale X, please see the Locale X release announcement. 10.0.357 is a minor update with the following improvements:

Workaround for an issue that could cause Application Not Responding messages on Samsung devices when running in the background
Improved location reliability for Crosscall Trekker devices in Australia
Performance improvements

Note: As a normal part of our release process to ensure high quality, updates to Locale X roll out in phases over a multi-week period. It may take some time before a specific update becomes visible to you.