They work......
It's a temperature sensitive strip that turns red when cold, not sure at which temp but at 40ยบ they are red, and white when warm. So you rub the strip with a hot sponge and it all turns white. The trick is that it cools faster where the liquid is on the other side on the metal wall, than where there's air. So for a few minutes there's a red section and a white section. The border is your fluid level.
So, you can't just open the fridge and SEE, it takes some action. Also, the keg has to be cold, again not sure how cold, to work. So it doesn't work for keggies that are outside the keggerator/keezer.
For the money I'm very happy. The only alternative I can think of is weighing the keggies, but that requires disconnecting and removing.....although you could have scales under each one with remote readouts...

..no, bad.....bad.....stop the voices......
