SpecFlow builds on existing unit testing frameworks like NUnit and MsTest. SpecFlow+ Runner is a dedicated test runner for SpecFlow (Windows only) and integrates directly with Visual Studio. SpecFlow+ replaces general purpose testing frameworks with a dedicated solution and introduces additional features, such as enhanced test execution options and execution reports:

Easier to use: Integrates directly with Visual Studio test runner (Visual Studio 2015 or later) and TFS build
Faster test runs: Support for parallel test execution (with different isolation options) and smart execution order based on the results of previous test runs
Better feedback: Create customisable HTML execution reports for your stakeholders, or output the test results as XML or JSON for further processing
More reliable: Detect flickering scenarios
More powerful: Define your tests just once and define test targets for your various environments (x86/x64, multiple browsers) to execute them on all platforms.
More versatile: Transform configuration files to set up your tests for different environments with placeholder support
More streamlined: TFS and TeamCity build server integration