EmotivBCI is now possible to work with an EPOC Flex headset but this requires a specific EEG sensor mapping same as the EPOC+ or EPOC X. You can achieve this by the following steps:
Connect your EPOC Flex with your machine (via Bluetooth or dongle)
Open EmotivBCI and click on the "Connect" button:
A popup will appear and you can click on the "Open EMOTIV Launcher" button to open the EMOTIV Launcher
Connect your EPOC Flex on the EMOTIV Launcher
Create a new EEG sensor mapping with a template (EPOC X Base Configuration)
Apply the new EEG sensor mapping
Back to the EmotivBCI, and connect the EPOC Flex headset as usual.