Biggest risk I have seen with soft chambers is CO2 poisoning in case of power failure. People can fall asleep while in the chamber and there is a power failure. Compressor stops ventilating the chamber, chamber remains inflated like a balloon without exchanging air with the exterior.
There will still be 700 liters of air available, but the building of carbon dioxide inside the chamber is a health hazard. In case of power failure, the OxyHelp chamber depressurizes automatically, door falls down letting the air come inside the chamber. So even when the patient is sleeping and there is no one around, it is totally safe.