A couple years ago I got a demo of an Ergotron adjustable arm, and have been using it every since. I like it a lot, but it isn't without its flaws.
First off, make sure you have an anti-stress mat to stand on. When I first started to use the arm, my feet became really sore. Standing all day on what was essentially a concrete floor with a few millimeters worth of "carpet" was too hard on my soles. The anti-stress mat relieved that completely.
Second, once you stand and raise your computer screen, you now have to raise everything else with it. This likely won't be an issue if your entire desk surface is up high, but whereas I have an arm that mounts to a normal desk it is something I've had to deal with. My keyboard, mouse, and monitors are at standing level, but my phone and anything else on my desk is down where I have to reach for it. Being in IT support, my primary computer (Windows) is on the arm while my secondary (MacBook) is on a stand on a box.
Third, standing takes getting used to, and eventually you will stand most of the time. However, sometimes you will want to sit. You'll want to have an option to sit down, whether it's an adjustable desk/arm or you can go somewhere else and work for a time.
Finally, and this is an issue mainly for my current solution with a desk-attached arm, be sure your desk/arm can hold everything you want. My Ergotron arm model is capable of dual displays, but the 23" Dells I use strain the weight limit of the arm. If I add anything more with any appreciable weight, the arm sinks down to the desk.
Overall I like my solution, and will not go back to a sitting-only desk.