I don't know why.. I thought that all 3 legs were adjustable and this thing would accommodate a large variety of sizes.. but no. The top one is adjustable. I was mounting this on the wall above my treadmill. So far, if the joints stay nice and stiff, I think we'll be good. I can angle it backwards so that the kindle is leaning back and it shouldn't jiggle out (since I can't adjust all 3 legs to get it in tightly). So, we'll see. I really wanted a clamp on type and all the clamp ons seemed too big. Now I see that this is too big as well. I'm sure it's fine if you have a big tablet. I just have an old Kindle Fire and it does it's job perfectly so I see no reason to upgrade. but.. well I guess it's too small for tablet mounts.