These are very high quality speaker stands from recognized brand K&M. They have a very rugged build quality and I would have no qualms loading them up to 50 KG. Made using proper steel parts, no plastics or aluminum.
The crank is great. It has a very smooth motion and has no problems hoisting a 35 KG speaker to about 2.1 meters height! Once up, it feels stable.
My only complaint about these is that there are no markings on the 35mm tube to indicate current height. It would be very useful to ensure that two of these are raised to the same height. You could of course do it yourself, but it would be a good extra feature.
To summarize, spend a little extra on your speaker stands and buy quality gear that will last a long time! The crank is great and saves you a lot of back pains. It also brings the speakers far over the audience, spreading the audio far and wide without issues.