Hate on cyberlimbs is new to me as well. They are even legal in the eyes of the law, so security wouldn’t think twice should they pick one up on their scanners.
They are legal, yes. But they are well known for having all kinds of tricks in them (like nasty concealed weapons or smuggling compartments), so they're more likely to get you checked over by security, especially if you're entering a secure facility. It also totally destroys 'corp drone' disguises. Maybe you could get by with corpsec, but having an arm by Renraku when you're posing as Ares corpsec? That's all kinds of red flags there, which means extra legwork adding it into your cover. A basic cyberarm won't cause trouble. A cyberarm with a deck in it, or weapons, or armor... well, that's another story.
Look, it is the same way that driving a shiny, chromed out Harley through an upper-class neighborhood wearing leathers is perfectly legal, but is likely to have people calling the cops on you. Heaven forbid you do that while being an Ork or Troll, they'll call HTR.