Yeah, probably half the internet has experience with GK tires. They are some of the most popular tires for mixed use and gravel over the last 10 years.

I have used the GK Slick for years in 32mm and one of my kids has 28mm GK Slicks on her road bike. They roll well, dont puncture frequently, and are relatively inexpensive. These are used with tubes.
Ive then ridden through multiple pairs of GL SS 43mm tires on my gravel bike. Again- roll well, durable, and relatively inexpensive. These have all been tubeless.

The consistent complaint about GK tires, and I fully experienced this, is that they are atrocious to set up tubeless. Panaracer's standards were horrible for years and the tires were entirely too floppy so it was tough to get the bead to seat on the shelf.
Panaracer just announced new GK tires with a full redesign, and its way past due. The new tires are supposed to actually set up easily on tubeless rims.
New models will be in 5mm increments, so 35mm, 40mm, and 45mm.

I am guessing there is a decent sale on GK tires because vendors are trying to get rid of their stock of the old models.