From this thread comment re spacers. I just wanted to chime in that I’m using them so far with no issues and cranks don’t seem to get loose. From time to time I get perhaps a few degrees of a turn in terms of tightening.
I do also have it on good authority (KH himself) that the use of them is a good thing on these new hubs.
The protector rings should butt up against the inside wire rings - so long as they’re snugged up but not massively tightened I think it is better than no spacer where the crank is free to work its way in ways.
Opting to not use spacers is in line with what Florian advises so you take whose view to trust here. Hub making, or crank designer (I’m using KH Spirits)