Seems to work as expected. One was not enough ...
344049
Seems to work as expected.  One was not enough for my 110 gallon but I knew it would not be.  I am using two so that if one gets stuck 'on' it will not overheat too quickly and if one fails altogether I still have some heating capability.
4224647
This one did not work , but the other works as advertised. I bought a replacement and expect it to work fine.
1135211
This item does what it says it will do, but I only received 1 in this '2 pack'.  Happy with the product, and I guess since it was very cheap I shouldn't complain about missing one of them. But when you think you are getting 2, it would be nice to get 2.
2485334
Received pack of five... using two.  One works fine, the other works for about two minutes and then stops.  If I turn it back on, it will work again for a minute or two.

Replaced battery on the latter one - it did not have the pictured TWO 2016 3V batteries, but rather ONE 2032 3V battery.  Seems to be working OK.

Any one of these attached to my Greyhound's collar serves to keep her visible from half a block at least. (By that I mean the light is visible - these lights do not illuminate the dog nor provide her a guiding light.

I'm glad I got these.  Shop carefully for the batteries - in packages of 50, for example, they can be dirt cheap. (21 Cents each.)  Package of two, not so much.

EDIT: Replacing the battery solved the issue with the one light going dark after a minute.
4173994
Seems to be working so far. Finding less and less of them now and found several dead in the traps. Will buy again if I need them.
1752148
Works fine.  Will get another one when needed.
2285005
I ordered two packs of two for a total of four (4) but only received a total of three (3) because one was missing.  They arrived quickly and work so 2 out of 5 stars from me.
4894601
I like this product fine.  My only complaint is I didn't need so many but I didn't see an option to only get one or two but the price was ok
4089822
One did not work, other one works great. Better to buy in bulk in case one does not work.
908215
Work well..looking at getting a few more spares
1676396
Ordered two. One was fine, the other was defective.
760508
It works.  Not much else to say.  I'd buy one again if necessary.
2053011
One worked fine, the other had a loose tape and didn't work. I only need done though, so it worked well enough for me.
3996042
Works as expected.  Worried about reliability.  Not the first ones we have used.  Two others failed though.
2171389
Product only fitted one devise. From add l thought it would install in several more. My fault....now have extra. Product works well.
3000267
Works great, should have looked closer at the description, I thought it was a two pack.  There was only one. :-(
3667912
Works as expected, but can't handle more than one larger appliance at a time. Example: Hair straightener on and laptop charging at the same time is a no-go. Otherwise, works great for charging up multiple small electronics at a time.