Seeing these for $25 - $40ish new on eBay.

These worth it for a simple red dot on semi-auto ARs?

Have put several on 22s and an SKS. They’re hell on coke cans at 25 ish with an very fast follow up. Never had one fail. They will run the battery down if you don’t turn them off. I’d call it a good buy in that price range.

I have one on a new Ruger PC9 and am very happy with it. I put up 3 of those 3" orange stick on dots and my wife, grand-daughter and I can keep our shots within those circles at 50 yards. I had to figure out which end of the red dot string to aim with because I have astigmatism in my right eye. Sometimes the dot looks like a starburst and sometimes a bit elongated. If I turn it down to where it is barely visible it's not as bad but harder to aquire. No one else sees that, just my eyes. I've got to go see the eye doc soon!

Believe or not - there are a bunch of knockoffs on Ebay. Why someone would knockoff such an inexpensive product Just make sure you get a real one. Plenty of info on Youtube to show you the difference.

I've had one on my 10-22 TD for several years. That poor carbine has been bounced around quite a bit and the TRS has never faltered. The only thing I don't like is that the battery life is pretty short. I won't buy another one because of the battery life. Luckily, I can keep a few extra batteries in the Magpul stock.

I have one on a Zenith SBR'd Mp5K...has worked perfectly in that config, cowitnesses perfect with the irons using a low mount...love it. Earl