They all seem to have "Three height levels" but what are they ? While the NEWlink is clearly the best value the range of elevation looks much lower than the Kensington. As ergonomic advice is to have the screen at eye level, a good idea would be to work out what elevation you need to achieve this and check that this is within the support arms range.
Some ergonomics pages click here
I went through a phase where I had real back trouble and I've used a monitor riser ever since and never regretted it.