I'll be the wet blanket.
I wouldn't buy one as a regular shooter or HD gun. Limited sight options, no easy options for optics, no non-clunky way to mount a decent light, certain springs and small parts can be a real bear to locate if HKParts.net or MGW don't have them, $80 magazines when they're in stock... and all three MK23s that I have shot have had absolutely trash-to-mediocre triggers at best. The match-grade accuracy, which I'll verify as an absolute truth, is completely useless. If you have a distance in your house at which you could exploit match-grade pistol accuracy, you should be using a long gun.
You get more capacity with a Glock 21 or 41, and even more still with an FNX-45. Both are set up out of the gate to run optics and WMLs. The Glock has aftermarket support out the wazoo, cheap mags, and an easy, well-established PMCS schedule. You can get pretty much any set of sights, any type of WML, and any type of trigger onto or into a Glock.
I would never say "don't" buy a MK23. They're a statement piece and they hold their value well. They're iconic. The quality is insanely high. But, as an HD gun, I would not recommend it to anyone.
Feel free to ignore my input, but I don't think a HD gun should have any "romanticism" to it. If it's a working tool, I want it to be predictable, boring, and most importantly, immediately replaceable. I get why some guys daily-driver El Caminos, but I know that if something needs to be replaced on my current-production hatchback, (a) someone local is definitely going to have that part in stock, and (b) someone local is going to have the equipment and knowledge to replace/install it. If it gets totaled in a wreck, I can replace it with basically the same thing, for the same price, pretty much same-day. That is far more important to me than having an emotional connection. Now, as a project car, a weekend driver, a show car? That's where a nice old car shines. But, it is a completely irrational daily grocery-getter.