I recently bought a Spigen Thin Fit 15 Pro case from Amazon for 19 dollars. This is my first Spigen case, so I can't compare it to what they were making 5 years ago. I can say that it feels very solid, and for what I payed for it I am quite happy.
It does feel perhaps a bit cheap in some ways. There are some seam marks in the TPU material around the corners that I can feel, though just barely. There's no fancy microfiber inner lining or anything. The case doesn't have Magsafe, though I don't use Magsafe so that was a non-issue for me (and in any case Spigen does have Magsafe cases that are also pretty cheap). But it seems well put together, fits nicely without being hard to remove (something that I consider to be important), and feels really nice in the hand. I basically bought it because my Apple Silicone case was a super dust magnet. The Thin Fit is better in that regard (as is to be expected) and I think the materials and design make it feel better to hold. I'm not going to drop it on purpose, and I doubt it would hold up to something like a Mous in a torture test, but it doesn't feel like I'm sacrificing much in terms of protection. The buttons also feel just about as good as those on the Apple case.
Maybe Spigen did cheapen their cases - as aforementioned, I don't really have any points of comparison - but hey, this was a cheap case. I didn't have to pay much for it, and for the price I think it's pretty good.
As a side note, I also got one of their screen protectors. The installation was perfect and it feels really nice, but it is a bit of a dust magnet around the edges so there's definitely some room for improvement with that.