Beats me. I've only been here a few months, but people are talking about it and I'm just curious enough to try.
A holo won't make it feel like a real arm, but if you don't want people to see it, then that's really all you need. Can I see it? Your arm? My BFF (gotta love the slang around here) has a custom prosthetic arm, from elbow down. It's a pretty complicated, beautiful piece of robotics. If I could marry it, I would.