Pros: I am in Canada.
-Cost is great compared to similar product sold locally.
-Tells the temperature.
-Sits in the tank instead of external probe.
-Clear numbers viewable from outside tank.
-Certain fish like to sit on this and hang out like betta and otos. Snails too.
-sticks to glass and acrylic tanks

Cons: -Build quality could be better
-some batteries that come with the thermometer might be pretty weak in power.
-battery compartment has a piece of plastic that pushes the battery into the contacts that is easily broken. I had one arrive that was already weakened and snapped right after putting the battery in for the first time.
-no ability to change it to display Fahrenheit if desired (That I know of).
-LCD display might be damaged. see other thoughts
-As with lots of other aquarium suction cups these are cheap plastic suction cups that need to be made of proper rubber. After being under water for a month or two it loses its flexibility turns white and you might have issues with it suctioning. Plan on replacing the suction cup after a couple years.
-face of the thermometer is angled maybe about 15 degrees away from glass forming a V. Because of this the display and area of glass around the display can become home for algae because I cant get my magnetic scraper in there. Otos might not go in there to clean the area.
-if you dont screw it down tight enough it can get water inside after a while.
-temperature accuracy can vary between different units and might be out by at least a degree.
-back of unit where battery compartment is could have been made smaller to save space.

Other Thoughts: I had 2 separate orders of these. The first 5 arrived and all but one were good. As mentioned the plastic piece in the battery compartment snapped while screwing the cover on. Another had a weak battery but not too big a deal for the cost. Since they were so good I decided to buy more. This second set of 3 arrived and one had LCD that displayed only partial numbers (display of 26.0 would look like 26.7) and one didnt even work.

Bottomline: For the price, you cant go wrong. Just hope you get ones that work flawlessly and are built well. They are not in the way by hanging off the outside of your tank like SKU 15704 which I also ordered. I will probably be ordering some more.

Pros: Okay, I didn't intend to use this thermometer in an aquarium. I use it as a regular outdoor thermometer - I just stuck it on the clean and wet glass. According to the manual, the precision is +/- 1 degC. I didn't have the possibility to verify this claim.

Cons: If you stick it on dirty and dry glass it will fall.

Other Thoughts: Put it in shadow to measure outside temperature - the black body will heat in the sun. It uses regular AG13 batteries - there are sold here cheap.

Bottomline: I haven't yet tested it in negative temperatures, but so far it works great.

Pros: Simple, nice looking thermometer.
I have no means to measure accuracy, but it gives similar readings when compared to other thermometers, this being in open air.
Suction pad holds the thing in place nicely.
Celsius degrees readings are a pro for me, but maybe not for others.

Cons: The battery compartment is quite prominent, I think it could have been flatter.
Also maybe a bit on the expensive side.

Other Thoughts: I don't even have an aquarium. But when I saw this cute little thermometer I suddenly had an idea - I would stuck it up the tiles in the bathroom, in the bathtub area, so that I can see the temperature while having a shower.
And it's been hanging there for nearly two months, immune to water splashes and working neatly.
By the way, I had to reverse the suction pad and I had a little trouble sticking it to the wall due to the prominent battery compartment, but once stuck, it has never dropped since then.

Bottomline: Even if you don't have an aquarium, you may want to give it some other use as a normal thermometer

Pros: This is a very nice in-water thermometer which in my opinion is better than having an external probe in the water. Construction seems fine with no apparent water leakage that I've noticed. The suction cup has not failed in the 3 months that I've had the thing attached (this is to an acrylic tank so it would be just as good on glass)

Cons: The only issue is that I cannot find a way to switch this over to Fahrenheit. My heater is set to 80F but the thermometer reads 24.1C (which is really close to 76F) Hard to tell which one is off but I would tend towards the heater since it's a analogue heater. It would just be nice to be able to keep it in F

Other Thoughts:

Bottomline: Great price for an in-water thermometer, you would be hard pressed to find anything better.