Note that the SK 28mm is only available for use with a tube. The 32mm is tubeless compatible. If you can fit it, I would recommend at least the 32mm for gravel riding.
I use the GravelKing Plus 32mm (file tread) on my gravel bike for those rides that are a combination of road and smooth gravel. However, I've taken them on some nasty stuff and they hold up pretty well.