Won't it still significantly add to the thickness, at least in terms of making one-handed typing harder?

IME it's pretty comfortable to use.

The sides can be made grippier and the back of the phone left slippery, so the in-out of pocket experience is nice, while the grippier parts fit in the palm when in use.

The added thickness on the border is also a welcome affordance, and as your fingertips are on the thinner back it feels thin still.

To me it's kinda the best of both world.

Have you tried it on this phone? Seems like it would vary from phone to phone as to whether it's a plus or minus.

I've long been inured to the Apple Tax, but that $60 plastic strap is taking it a bit too far IMO

Yeah especially because it's not even compatible with the Apple Cloth, for when it gets dirty.

...unless it lands on the big protruding camera lens.

That's fair. The corresponding full-body case Apple is releasing for $49 does have a conspicious extra lip higher than the camera bulge (albeit that's typical to mitigate camera flash glare). https://www.apple.com/shop/product/MGH24LL/A/iphone-air-case...