I bought these suction cups a while back because I was adding a bubble wand to my 75 gallon tank.I wanted the wand centered in the tank,but I couldn't keep the tubing buried deep enough to not pop up and show,to where all could see it.
That's where these little guys came into place.You can now run tubing, plants hanging from the top of your tank down,or anything else that fits between the suction cup's holding space,and have a much cleaner looking view. I run the tubing down the side of the tank,and over to the middle.I use these to "place" it,and it's a done deal! No more tubing popping up!
I also like those long flowing plants at the top of my tank.My Plecos breed constantly,and the babies get eaten because they like going to the top of the tank,where they can be seen by the bigger fish.
I stuck a suction cup up at the top of the tank,and hung a long flowing Bamboo Plant from it,and it's worked great!
A simple product that helps an awful lot with aesthetics.

Pros: cost friendly easy to find

Cons: none that I could see.

These worked for awile, but i had to constantly keep putting them back onto the glass. I used them for the bubble wand and i didn't care for them much.

Pros: Inexpensive

Cons: Don't stick very well