Might be different for different people but I sure prefer a "open device using a proprietary file format" over "proprietary device using a open file format" as the former allows me to change everything regarding the device, even what file format it uses. So I can continue using the proprietary file format or change it to a open one with a different reader/writer, but same hardware.

"proprietary device using open file format" would make me be stuck with whatever format they decided to use, and stuck with the same reader/writer. This is less helpful to me than being able to change everything in the device.