Complex sentence: Fixed barrel models have a "Tropical" MP5-style handguard with ventilation slots and quick-change barrel models have a four-position Picatinny Rail handguard (usually used with a vertical foregrip).
Split into simpler sentences: Fixed barrel models have a "Tropical" MP5-style handguard with ventilation slots. Quick-change barrel models have a four-position Picatinny Rail handguard (usually used with a vertical foregrip).