I had three real problems with these and two relate to how they attach to the desk. The first is that my desk is next to a window ceil. The extension up would have more than likely hit it. The second is how it attaches to the desk. My desk is wooden and not stressing the wood is a priority for me. Additionally, the lip of my desk is short and curved.
The third and most important reason is that most of them don't hold a keyboard. The ones that do, aren't very atheistically pleasing either.
Do It Yourself
After looking through other options and knowing that spending another large sum of money wasn't on the table, the DIY option seemed like the best for me. It took plenty of research but I eventually came across this IKEA standing desk. Beyond the fact that this is an excellent post about standing desks in general, it's also very flexible for everyone. Since you can adjust the height of the bookshelf mounts to fit your need, it really makes it an option for most people.
For the first few weeks, I used velcro cable ties and lego blocks to determine the best location of the shelf before attaching it the table. Reading the comments, there's a suggestion to use bolts and nuts instead of screws. Not reading that until after the desk was assembled, I used screws. They are working fine for me, but I also attached the brackets fairly high and it seemed the top screws were going into some solid wood.
I also added velcro to the bottom of the feet to keep from scratching the top of the table. Since IKEA is over an hour from me, my only regret is having not gotten two side tables so the desk would be wider.