I bought this for astronomy use, but this will probably be the first thing I have ever returned to Amazon. This thing is really cheap. Considering you can get a pretty decent aluminum LED flashlight from Home Depot for $3, I was surprised at how cheaply made this one is for $5. Its all plastic and not very sturdy feeling. Its is actually really large (about 3.75" long, 1" diameter, measured with digital calipers.). I thought it would be tiny, but that clear dome you see in the picture isn't the LED, but a big plastic cover over the LED. The picture makes it look smaller than it is. The funny thing about the size is that there's nothing really in there. The battery compartment extends about .75" into the housing and then ends. There is nothing else going on in there.
Also, mine pretty much doesn't work. It worked when i first got it, but then I popped off the cover (easily done) to check out the battery compartment, and when i put it back on it was significantly dimmer and intermittent. I opened it up, removed and re-installed the batteries, and it still didn't work properly. I tried this a few times, and it just didn't work. The batteries were clearly facing the right way, and the electrical contacts were clean, but honestly the contacts on the light side are just a thin wire, so I'm not surprised that it isn't more reliable. I actually build robots for a living, so I know how to install batteries in a flashlight, but no dice. After messing with it a bit more, it seems to be bright again, but its intermittent, and honestly I don't want to deal with it. Its not even easy to install the batteries the right way, because the cavity is large enough that they can easily flip over when you drop them in. You have to try a few times to do it, and as another reviewer said, it would be a real pain to do in the dark.
As a mechanical engineer who designs things all day long, I am particularly surprised at how much is wrong with such a simple device. I think my mistake was searching for "Astronomy Flashlight". I realize now I should have searched for "Red LED Flashlight". That comes up with a lot more options. I might try something like an Inova Microlight (I'm not affiliated, but they just came up with the new search terms i mentioned, and I've seen that kind of light before and liked them). I will probably just go to Walgreens or some other drugstore and pick up a red keychain LED. I've had pretty good luck with those in the past.
So really, search some more, and try something else. I saw a few negative reviews and figured it was a fluke. Now I've realized I shouldn't have been so optimistic. I imagine they won't all be as finicky as mine, but I can't imagine it being worth it to try when there are plenty of other options out there that are better made and more compact.