With Split Personality, Windscribe rotates your user agent between the most common ones out there, to reduce the chance of basic fingerprinting.
Each browser has what is known as a "User Agent" which identifies what operating system you use, and the exact browser version. This piece of information is available to every single website you browse, which can be used (along with other things) to uniquely fingerprint your browser and reduce your privacy.
Keep in mind this feature will not eliminate advanced fingerprinting (https://coveryourtracks.eff.org/), since the browser extensions don't have access to certain browser functions.
You can enable the Split Personality feature from Preferences > Privacy > Split Personality.