My main issue with standing desks (and most regular desks actually) is that I like to have the keyboard relatively low (forearms parallel or slightly downward) and the display at eye height (well, top row at eye height, maybe a bit higher); most screens don't go this high. Luckily most of my workplaces have had printers, and where there's printers there's the best monitor stands you can get: packs of A4 paper ;). Anyway I need a few more of those for a standing desk.
I'm not a fan of actually supporting elbows, that (for me) would lead me to leaning on them, which leads to 'hanging' and shoulder / neck issues.
When I had a sit down desk, I always tried to get desks with the keyboard pull out draw.
I also much prefer having the keyboard / mouse low, but then I just adjust my chair to also match that height so my forearms rest naturally.
Funny enough that's exactly what I used to prop up my monitors too. It's so good because you can fine tune the height by just removing a chunk of sheets.
If you sit up straight, the weight should be pretty evenly distributed. It felt like floating on air.
In the end I guess that's what matters. Try to find a set up that puts absolutely no strain on your forearms, wrists and hands.
I'm not a fan of actually supporting elbows, that (for me) would lead me to leaning on them, which leads to 'hanging' and shoulder / neck issues.