This is an interesting way to turn a classic science experiment into a functioning addition to a fish tank. It makes a pretty cool display!
Be sure if you try this to have plenty of water circulation in your tank or the water in the suspended area could become oxygen deprived.
The physics in the way this works are relatively simple, as the water seems as though it should pour out into the rest of the aquarium, but seemed suspended in mid-air; however, if that were to happen, you would be leaving a vacuum in the jar.
There really shouldn’t be any problems if the tank is well functioning prior to adding the new compartment. You may also want to put a wide base of some kind below the supports so the extra weight is spread over a larger area and you won’t risk cracking the bottom of your tank.