I love my standing/sitting desk. I use an uplift from thehumansolution. I've been using it for about 8 years now. I bought one of their frames only and removed the desktop from my old desk to mount on top. I'm not sure if they sell just the base anymore, but I see they have a lot of options. I also use a lifespan brand walking treadmill under mine that I've been using just as long. I highly recommend both. It has done wonders for my back issues that kept getting worse after prolonged sitting.
It is not wobbly, and I have my entire desktop and triple monitors with heavyduty tri-monitor base on top of it.
Seconding uplift. I bought directly from them, I'm not sure how or if that impacted the price. Very sturdy materials with a long warranty (15 years I think) standing behind their products.