They work, as well as they work. I've got quickjacks because I don't have a strong slab or enough height for a proper hoist.
For some reason I don't have many good side on pics but this is the idea.
It lifts it higher than regular jack stands but still not very convenient. According to specs in mine the frame is 462mm, plus whatever you add as support blocks (I use rubber blocks about 100mm high at each corner, so about half a metre of clearance)
There are similar style scissor lifts which do lift higher, to say 1 metre which might be the case for what you've shown above, but it is still nothing like a proper walk under hoist
In terms of support, you just use rubber blocks between the top of the jacking platform and the factory sill jacking points.
The style I have, you park the car and then slide the jacks under so clearance is no issue. If you get a style you need to drive onto, consider clearance from the front bar to the lifting platform, depending on how low your car is you might only have 100mm to play with
Keep in mind, you do get clear access under the car eg to gearbox, exhaust etc, but you can't access anything around the sills (eg rear subframe mount), and you can't get under the car from the side, you need to go from either the front or rear of the car