It's not just that they're not worth their money, they're not worth it in general. The nozzle that simply attaches and doesn't screw onto the bottles is not user-friendly at all, and the bottle doesn't stand properly, it is unstable compared to the simple and cheaper ones of the same category that screw on.
While I followed the instructions and used plastic water and soft drink bottles, they would empty immediately or not at all.
Waste of money, I do not recommend trying them.
The simple "Gardena Watering Nozzle with Droplets Drop to Drop" and much cheaper ones that I bought and used with a glass bottle of vinegar or soft drink work well if you water properly.

They seem to have a higher quality construction than others of the same kind, but in practice they are not. Some empty the bottle the same day while others keep it for 10 days..(being set at the same flow rate). Very expensive at 18 euros, I wouldn't even consider it. Maybe at a package price of 6 euros I would buy it again.

When the flow is set almost low, the 1.5-liter bottle empties in 2-3 days and overflows the plant saucer.
With the flow set to completely low, it seems like it's not running at all.
Overall, it is a higher quality material compared to other similar ones, which also empty the 1.5 liters in a day,
but because it is much more expensive, I would not recommend it.

I tried it this summer while I was away and it seems to work. The plants were preserved just fine.