This little laser post deals only with SD 30x, as in SD 301, SD 302, SD 303. I have held eight or so, I think all advertised as < 100mw.
A product page typically shows them labeled (for example) ‘SD 303’, but you will likely receive one labeled ‘LASER 303’. Sometimes they arrive without keys, so I have made a few fairly easily. I’ve never seen one with O-rings. There is some variance in the brightness, but I consider them all quite powerful. Less than half a second to burn tiny holes through black or grey polyethylene grocery bags. Not a child’s toy, they should be treated as dangerous - I expect one would quickly damage an eye. Whoever points them at animals is an anus. Not powerful enough to do anything useful like cut pipe; far too powerful for a classroom pointer. I don’t know any practical use.
That said, I claim them among the best money I’ve ever spent. Handled CAREFULLY, they can amaze and entertain a group for ten whole minutes. Maybe twenty minutes if there’s beer.
The main tube is threaded two sections, so you can use 1xCR123A primary, or 1x18650. However otherwise decribed, the button side switch is momentary on, which is good for safety. The laser stays on while you press the button, but if you fumble or drop it, the laser turns off. I imagine minimal heat-sinking, so have never kept one on for a full minute. A knob on the business end can be unscrewed/extended to defocus/spread the beam up to 2 to 3 degrees to make a spot. Green appears the most luminous, then red, then blue.
For now, I’m convinced the model designators are like this:
301 = knurled tube
302 = smooth tube
303 = 301 plus extra knob on the end, which is a ‘filter’
I recommend the 303. Removing the ‘filter’ makes a 301. Leaving it in place makes things safer around people or indoors. Variously described, this ‘disco filter’ attachment spreads a broad field of four zillion small images - the best is simply some kind of dot or star - others available are hearts, smiley faces, etc. Rotating the filter makes the images coalesce into half a zillion brighter ones. Maybe useless except as huge entertainment. Wait, I mean for the kids.
So far, all the less than $10 ones seem out of the same grab bag as the more expensive. I’m still waiting for my first buy of green, red, blue from GearBest. $7.64 each.
I will not trust any notion that my cheap lasers are blocking whatever IR component.
Anyway, the longer 303 fits well in this pouch