I use an Axis-49 which is my primary midi controller at the moment. The small 49 key version feels kind of like a cheap computer keyboard. The velocity sensitivity okay be very non-linear. I haven’t taken the thing apart to see if any of the components are identifiable.
No idea if the larger 64 key version used the same or better key mechanisms.
Looking at the above image of the key construction I see that it is likely that velocity sensing done by calculating the delay between the outer contact losing and the inner contact closing.
This project is not the same as the axis but possibly of interest: