As a point of Biology and Bionics or well Mechanical Devices of today (approximately the year 12'000 or 2'000 of the Holocene and Gregorian Calendars respectively). We have scientific studies on the inputs and influences of neurons (from a rat or mouse I believe), on a mechanical device with a programme. The programme is a flight simulator and basically the neurons learned over time how to manoeuvre the plane through electrodes in the device. IF IN 40k there was a way for biologic energy to re-initialise a bionic eye or general body-part or (because WE MUST still have a human brain), we have human neuronal RESTANDARDISATION techniques that would alter the neuronal activity to a bionic part to better control and interface with it. Then there should be next to no real problem for human control of the devices.
But for boons to having bionics, I would imagine that even for astartes a bionic eye for instance would add potential customisation AT LEAST.