Hard to find Blackhawk serpa holster for 3.5 XD. They are usually for the service or tactical size. I found a Fobus holster that fits 3.5 really nice and snug for a owb. and it is just as good and cheaper.
IWB I would go with a Crossbreed, but can be $$$
Serpa are not exactly good for concealed carry. They stick way away from your body and print badly. They are as thick & cumbersome as the XD Gear holster that comes with your XD. A good rule of thumb is that if the holster hooks onto your belt & is made of plastic, it is not good for concealment.
If you need a ccw holster, buy a High Noon OWB, or a Comp-Tac MTAC. That will bring the pistol close into your body so nobody will notice you have anything on your hip.
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