I've been watching
this thread since release and I must say I'm pretty skeptical about how much damage is claiming to be done from the dock.
I'm definitely erring on the side of caution when sliding it in and out, but I think it's a bit too soon for the all panic in that thread (the homemade docks, people not opening their Switches...). I'll be careful and I honestly think I'll be fine. I'd be really interested in looking at that thread in a week to see how many people are scratching their screens from the dock.
Spending $15 on a tempered glass screen protector doesn't sound too bad at all though; it's certainly worth the piece of mind and will surely help protect the screen from a lot of things.