Legally I’m not sure why this would differ from a fanny pack or other concealing bags etc. As long as you can’t see the firearm it is concealed.
During the height of the fanny pack craze a lot of us carried in them. Because of the size and construction of fanny packs designed for concealed carry someone who really looked could tell which ones might be holsters (e.g., maybe spot the odd edge of material that hides the velcro). But that takes real effort and expertise, and just didn’t happen with people walking down the street. The same can be said for all forms of carry, occasionally you will have an unusual lump show briefly (e.g., when you bend over) even if nothing looking like a gun is ever visible. Someone in the know may suspect, but it takes a pretty big leap to go from mentally realizing “that’s a bit odd” to screaming “GUN!”.
My problem with the SP is that just as fanny packs have gone out of style as general street wear, they look odd and thus attract attention. So they may be perfectly good (and legal) forms of concealment, I’d rather not have something that draws attention to where I’m concealing my gun.