First and foremost drawing the pistol without flagging yourself and everyone else is pretty darn difficult. Additionally when your draw stroke requires you to place yourself in an armbar (i.e. the hammer lock) to get your pistol out you should probably re-think your gear.
Re-holstering is a nightmare, because your support hand is probably going to need to clear the concealment garment out of the way, and we kick off the chain of events known as the “two handed re-holster” and a gunshot wound to the support hand.
That bump at the small of your back will print in any position other than standing upright. All holsters will print in some specific circumstances, but unlike other holsters there really isn’t a way to camouflage this with an arm or a hand.
Having a lump of metal at the base of your spine will make sitting uncomfortable and the gun very difficult to access from a seated position. Falling (or getting thrown) on to your back will only make your chiropractor and your assailant happy. In a fight that goes to the ground you are going to have a very hard time getting to the gun from a supine position.
Retaining the holstered pistol is going to be tough because it is much harder to get a hand on the gun for the wearer than it is for an assailant that is approaching from behind. That hammer-lock draw stroke isn’t going help either.