Like pretty much all AppExchange apps, in order to use Flexpricer functionality, users need a license.
However, Flexpricer extends standard objects (Opportunities/Opportunity Line Items/Quotes/Products/PricebookEntries etc.), so any records that either you, your users or Flexpricer creates in these objects are accessible to your Salesforce users irrespective of Flexpricer license status.
For example, Flexpricer always writes the total quantity of a line item in the standard Quantity field on Opportunity Line Item / Quote Line Item. It always write the sales price into the standard Sales Price field and the finally calculated discount in the standard Discount field. So this data is available to users, whether licensed to use Flexpricer or not.
The data used by Flexpricer to calculate and set the correct values in the standard fields is stored in Flexpricer custom fields that requires a Flexpricer license to access. E.g. the information that triggers adding on a line item because it’s part of a bundle, or adjusting the price/discount as a result of volume pricing is stored in Flexpricer custom fields stored on Flexpricer custom objects and is subsequently written to Flexpricer custom fields on Opportunity Line Item / Quote Line Item.
If a user does not have a Flexpricer license, then they will not be able to access Flexpricer custom fields or Flexpricer custom objects (such as Volume Prices, Bundle Relationships, Account Prices etc.). And, they will also not be able to use the Flexpricer interface to manage line items.
So, if an unlicensed user was, for example, to use Salesforce’s standard Product Selector interface to add a product as a line item to an opportunity (rather than the Flexpricer interface), then the line item would simply be added as standard Salesforce behaviour. No Flexpricer-specific data would be considered, calculated or written to the line item because the user is unlicensed and is not adding the line items using the Flexpricer interface.
If Flexpricer was subsequently launched on that same opportunity by a licensed user, Flexpricer would consider the line item as just a standard line item without any Flexpricer functionality applied to it (such as knowing that the added product was actually part of a bundle). This could give inconsistent and unexpected behaviour to the licensed user.
For this reason, we recommend that all users who interact with opportunity line items and quote line items are licensed for Flexpricer and use the Flexpricer interface for managing them.