I'm standing at an Ikea Bekant sit/stand desk right now and have no issues with wobbling. I also only have an laptop, external monitor, two bookshelf speakers and a small lamp on it, I can see how a monitor arm might cause wobbling. I've had it for ~3 years, moved it a few times and never had any issues with it. At the time it was far cheaper ($500) than any other sit/stand desk on the market, not sure if that has changed.
Also going to chime in and say I've got one with monitor arm (only one monitor mind) and bookshelf speakers (also not a lot of weight). No wobble after 2 years or so.
When assembling I did feel that the actual attachment of the surface/board was a bit cheap. They used plastic positive tension pokey... things. Not sure what you call those. I suspect if you have to disassemble / reassemble it a few times they may wear out and the top may wobble independently of the base.
