A common pattern is to use variants within Formsort, which each can have a unique URL, together with an upstream testing tool, such as Optimizely, to track experiments. Using a third-party experimentation platform allows for experiments that span across Formsort and upstream or downstream parts of the user journey.
Flows have their own URLs, and can be pointed to by a custom domain, which does not require a variant to be specified.
For quick experiments within Formsort itself, you can assign weights to individual variants from the flow index page.
If a flow has two variants, and variant A has a weight of 50 and variant B has a weight of 50, then when the flow URL is loaded, half of the responders will be sent to variant A and the other half to variant B.