The only concern i have about flaps is that they end up curling up or deforming inside the pocket from pressure the tissue puts on them, or an installer not making enough room for them under the dermis and they get folded up. That would create cavities where blood doesn’t flow so well (or maybe not at all) and the inevitable biofouling that could occur there could mean serious medical complications. Malicious bacteria roam freely around the body and are mostly ignored, but once they have a place to safely set up shop, they will establish a colony and create biofilms to mask their presence from white blood cells, and start kicking out all kinds of junk proteins and waste that can cause serious illness and in some cases even death.