I carried one for 5 years in an SS-III holster and the weight of it was felt even in that rig.
It was given to me by the department upon retiring but I would not see me buying one on my own.
It fits my hand and I shoot it well enough but for a concealed carry weapon it is awfully big.
I have carried it a few times in cooler weather under a jacket or sweatshirt and it is comforting but big and heavy.
Like retsupt99 says it is perfect to keep bedside but like him I have a G-36 for when I feel like carrying a .45 ACP.
My G-23 is my primary carry and I feel it will do what the G-21 will do in a smaller package.
If the ones you are looking at have night sights and 3 high cap mags and in good shape then they are worth $400.