This subject is fairly convoluted in design. For example if you plan to get a license for yourself while developing flows for your company you may run into an audit situation.
If this applies to you, you'll need to understand that how Microsoft determines licensing for flows is based off of triggers and not the actual premium connector.
i.e. If you have a flow that triggers off of a form, that form then updates a ServiceNow ticket. Whom ever has the ability to submit to that form would need to be licensed, per microsoft.
Now, if you're just a individual licensee, then the monthly premium is all you really need unless you are doing some hyper specific tasks. And typically the free version itself is pretty solid for majority of everything else.
