It fits perfectly on my radiators (old type). When I screw/unscrew the radiator for ventilation, I do it carefully and do not use force so it doesn't break. Very good for ventilation and you avoid splashing. It makes your job easier. Recommended.

The quality of construction is good. The key does not fit perfectly, I think it should have been a little longer

Very good. It facilitates incredibly.
The only thing I wonder is why they made it so small.
The part/container that fills with water could be three times bigger, lengthwise (because widthwise, I understand it would 'hit' the wall) and a little deeper. Why should I empty it 2-3 times for each radiator, when one time would be enough... if it was slightly bigger?
While it is very good, this little issue seems to reduce its usefulness.

I got it all excited. On the third use, the nozzle broke, something I have never experienced before. I don't know if it was defective, but I was completely disappointed because firstly it cost me money and secondly I didn't get to enjoy its practicality. I mention this fact so that it exists as information for any potential interested party because if someone had mentioned this, I definitely wouldn't have bought the product.