I went from all covered up (silicon apple case, Zagg screen protector and ASK) to just an ASK.
Both on my 12.9 (1st gen) and 10.5.
The reasons are simple.
I write a lot, both on my 12.9 and on my 10.5 Having a glass screen protector makes it slippery as a wet tiled floor. It makes my writing even less readable, even for the Nebo app, and makes for a more cramped writing. So out went the screen protector.
I had the silicon case on my 12.9 and 9.7 but it makes it a bit sticky when I want to stow them both in my Goruck GR1 laptop compartment and even more so when I want to get one out. Then I also got the Yohann iPad stand, which I really like a lot, but the first version was only usable without case. So of went the case.
So now I only use the iPP’s with ASK, but when I want to read a lot I click the ASK off because it’s more easy to hold and lighter without.
When transporting them both I put the ASK against the AKS and have the aluminium back outwards. It then slides easily in any laptop compartment.
I do clean the “suede” side of my keyboards a lot as that touches desks/tables/what ever I’m putting my iPad on to prevent grains of sand scratching my screen. But so far it goes really well. My 12.9 is now about a year naked and has no scratch, the 10.5 obviously has had much less time being naked but it also is still in pristine condition.
Only worry I have is that it drops and might damage. But then again I have apple care + so it’s a financially limited risk.