IMHO the serpa is a poor "concealment" holster. It conceals in winter with a jacket. Otherwise it is mostly a no go- you piece prints bigtime.
I think that depends a lot on what degree of concealment you need.
Those of us that OC regularly are well aware that short of putting a big flashing neon sign over our heads saying "Gun HERE!", the majority of people will never notice even an unconcealed weapon. People just aren't that aware.
Even when I'm concealing, I regularly just untuck my shirt and let it hang over my Serpa. I'm not just printing -- the bottom of the holster normally sticks out below my shirt! And yet I'm hardly ever "made". With a longer shirt or jacket, I've never been made, that I know of, even though it prints pretty badly.
I agree that if you're really concerned about concealment, then you may need to go with an OWB holster that holds the gun tighter to your body, or even and IWB, or maybe even real deep concealment, like a SmartCarry.
Concealment is a continuum, not a boolean value. What holster you should use depends on where along that continuum you need to be.