Why ISO to 1.6 Million? Same as Nikon D500. If no useable image can be created at that ISO, then why state it.
Advertising copywriters want to state such things in a game of one upmanship.
It reveals a frantic desperation by a company to Sell cameras.
Who does it bluff? The not- knowledgeable buyer who is impressed by such specifications.
A silver tongued salesman will pull the con job to make the buyer choose camera A instead of camera B by pointing out such "specifications".
A long time ago, a similar scam/fraud was perpetrated on ignorant buyers of film compact cameras that boasted "Panorama" specifications.
When in fact all that happened was two pieces of plastic slided over the film image's top and bottom.
It was fraudulently misrepresented as a top end & much sought after "feature".
But other than that, K3 III is good. Especially for those who own vintage Pentax glass which are pretty respectable.
Pentax is a manufacturer that covers APS-C, Full Frame, Medium Format.