With this I can always tell when my fish are comfortable as long as it's "in the green" I call it. It is made of glass though so it can break mine had a small break in it and it still worked though, so it's a lifetime thermometer if you are careful not to break it!

Pros: I can always tell when my fish are comfortable

Cons: It can break

This worked after having five different goldfish, the last one lasting over 7 years. The only problem was that the suction cup didnt stick after a few months, but I bought a new one and that worked fine.

Pros: worked well after about ten years of fish

Cons: suction cup didnt suction after a few months, but I just had to buy a new one

I used one of these when I first got my aquarium and found it very hard to read through glass and water.

Pros: keeps accurate temp

Cons: Hard to read

I have 7 or 8 of these. We use them in all our tanks, I use them to check the bath water temp for the snakes, hermit crabs, and iguana.
I use one to occasionally check the water bowl in the crabitat for our hermit crabs, and drinking bowls for our snakes just beause I can, the drinking water doesn't vary much.
I really like these, just don't them on a hard surface as they will crack :-) Very convenient, very effective. Some of mine have been around for years and still check out as being accurate when I test them against new ones.

Pros: We use it for lots of different things

Cons: Can't think of any

This is a very simple thermometer for your aquarium. It keeps accurate temperature reading and shows the proper temperature range for tropical fish. Mine never stays attached to the glass wall and I usually find it floating around.

Pros: Accurate reading

Cons: rarely stays attached