What's the working principle behind telescopic tube

They have three versions. One seems to use a motor and lead screw controlled with a pushbutton arrangement. Another is limited to just two positions locked into place with a lever or similar device. The final version has some sort of escapement that locks it into two positions without a lever. The two position versions likely have counterbalance spring.

"...You have the choice between stepless height adjustment using a button or primarily upper and lower fixation using an operating lever or click-clack function. Our click-clack function is particularly convenient because it does not require a lock and can be brought into the upper and lower position by slightly lifting the tabletop"

Which of the three versions are you interested in seeing?

Thanks, a 2 position will be fine (750 - 1100mm).
I definitively want to go low tech (using an handle like the link provided).
My concerned is:
- 2 tubes that match are not easy to find on the market, and I can't afford to order custom tube because the quantity are too small. I planned to use ring to cover the gap beetween the 2 tubes diameter, ie 100 to 114mm, but should it be plastic or bronze?
- How can I fix the ring to the tube (screwed?)
- To action it manually, I then need to design a gear and a lead screw with a crank (like on the animation provided in the link)
- Due to the weight (worktop + mechanism will reach 40Kg), I will need a reduction gearbox and not a simple gear, so that's becoming tricky and expensive.