I too rock climbed for a number of years before I got too old for it and put all my spare time into archery and hunting. AFAIK, a screamer comes built into all tree strand harnesses that I am aware of. It consists of folds of material that will rip apart on impact to cushion your fall. Not so necessary in a long fall on a climbing rope, that stretches and where the belayer can ease the rope out to cushion the fall, but essential for the short falls that are likely from a tree stand, in order to avoid broken bones from the impact. When I was climbing, a screamer was not included with a climbing harness; you had to buy one separately.
Second, tree stand harnesses are designed so you end up right side up after a fall. For a young fellow, being upside down in a climbing harness is no big deal after falling on a cliff face, although I usually managed to stay right side up anyway, but hanging upside down could be a bigger deal for an older hunter carrying a few more pounds.