Thanks for all the replies.
From a tech pov, the processing and RAM are ample for my purposes, even for the occasional big sums and transformations I do. The screen size and performance are superb, and the keyboard and trackpad are just right.
Battery is now 88% on a Cycle Count of 327, which I worry about, as I don't recall being that low on the 2015 MBP. I'm half-full on the 1Tb of storage, so I might have a spring-clean as I know that will fill up over the duration.
Of course, the longevity of the M1max chip is not yet known, and as mentioned Apple will eventually decide that it will not support their latest o/s upgrade. The other unknown is the 'must-have' technology advance.
I had clung to my mid-2015 15" MBP for a while and still recall the excitement in the run up to the announcement, purchase and then arrival of this 16" beast. At that time, I delighted in the keyboard but wondered whether I had splashed too much cash going for the M1max. However, it has replaced my need of a desktop m/c and I have the sense that this will continue to make me happy for at least 3 to 5 more years.
My only itch is the weight. At one time I thought that I could use an iPadPro for travel, also minimising the risk of loss of my main workhouse. But even with keyboard I did not enjoy the haptics - nor the added weight. My use of that is now very occasional. (I confess that I am keeping an eye on the much lighter MBA with its M+ processor for travel use.)