Definitely harder plastic than silicone, but still a somewhat flexible plastic. It’s a decent thickness, and a little slick I guess, but never difficult to grip or anything because of the loop.
They only sell them on their website, but they do offer a 30 day return policy.
I never order the screen protectors from there. I buy the case, and pick up an extra loop ($5) to get free shipping. I figure it never hurts to have a spare loop (having one to do a makeshift loopy til my case arrived has been a lifesaver since they were shipping so much later than the new phones).
I’m obsessed, and I’ve never known anyone to buy one and not like it. I’ve gotten most of my family and some friends hooked on them.