I believe the idea is that it is you essentially get the best of both worlds with this setup because 1) switching between sitting and standing is more fluid, as you need only to sit down or get out of your chair to switch (rather than needing to change desk height) 2) it is in general cheaper and longer-lasting because there are not motors, etc. involved.

If all you are trying to accomplish is to move from sitting/standing while working at a computer, they solve the same problem in a way that has been solved for at least a hundred years and is generally cheaper.

There are some merits to adjustable desks above and beyond that though.