Atos Provox FreeHands Flow HME Cassette is used For the FlexiVoice Speaking Valve. Provox FreeHands FlexiVoice offers both the freedom to speak hands-free and with finger occlusion when wanted. For hands-free speech you can choose between 3 different strengths: light, medium, and strong. The choice depends on how much airflow and pressure you need for speaking and breathing.