I haven't had any problems with this thermo. I find it easy to read. It stays stuck to the side of the tank. Perhaps if I had something else to compare it to like a digital, then I might have a different review. It does leave water marks around the suction cup.

Pros: easy to read

Cons: suction marks

This is a great cheap little thermometer to use if you need to check your aquarium temp often especially like I do. I need to keep it at a certain temp to allow proper breeding and birthing...so this is a very accurate reading from this thermometer.

Pros: cheap and accurate

Cons: N/A

I have quite a few and have never really had a problem with them staying in place. I will say that sometimes when they're new,that it's a bit harder to accomplish,until the cup softens up some.
Overall,I really like them.

Pros: Stays suctioned to the glass-accurate reading

Cons: none

Other than the cheesy suction cups, the glass therometer is reliable if some what fragile.

Pros: Low cost

Cons: suction cups fall apart

I've had the same thermometer for years. I have it suctioned to the front of the tank and it is very handy.

Pros: Hard to read if it isn't turned just right

Cons: Seems very accurate