I've been lurking on this thread for a long while, and finally bit the bullet ... ordered a K1 Max 80% (i.e., TKL). Brown key switches.
If I don't like it, I'll be offering it for cheap on the marketplace of this site.
My motivating influence was that I wanted a TKL so that my right hand doesn't have to extend as far to reach the mouse. In some ways the 75% looked better, because the function keys are closer together, but I didn't want to relearn my muscle memory as to where the home, end, delete, and page up and down keys are.
I had an old Unicomp keyboard back in the day. I like the low profile of the K series over the regular profile of, say, the Q series. I went to Staples and mashed on the Logitech mechanical keyboards they have on display, and liked the clicky one better than the non-clicky, hence my decision to go with the brown.
I actually don't mind the newer Apple keyboards, but wanted to try out a mechanical keyboard. My biggest concern frankly is that I've really gotten used to having Touch ID on the keyboard. But, I wear an Apple Watch, so hopefully that'll serve as a decent substitute.
Was going to wait for Amazon to stock the K1 Max TKL ... right now they only have the Pro. However, I'm traveling in a few weeks, and wanted to have the new keyboard to try out when I'm overseas (bought the carrying case too).