Going to go against the grain here - was thinking to myself just the other day how pointless these are.
I have two DC, youngest is nearly 3 and still in nappies, we change him either with the nappy mat on the floor or on our bed. It may be that with your bad back that won't be doable, but bear in mind that if you have a changing table you are going to have to lift baby up and down onto that every time you need to change the nappy. That's ok when they are newborn but they quickly get very heavy (or at least mine did). My sister uses an ordinary table with nappy mat on top if you do need the height.
The other benefit of changing on the floor/bed is that it is so much easier to interact with them and play games during nappy changes, as you are facing them and leaning over them. When I used a friend's changing table I was surprised how high it was and hard to interact. You are often also sideways to them (with the changing table pushed against the wall).
Finally there is the risk of them rolling off the changing table which makes nappy changes more stressful. With them on the floor I found that from about 2 months old they would be happy to kick there for 10 minutes while I pottered off to find wipes/do jobs.