It is extremely solid! I'm using a 40mm solid extrusion, so it is also pretty heavy. Because it is aluminum, it is not as heavy as it could be i guess.
There is a deflection calculator
https://8020.net/deflection-calculator, and even if i put 300 lbs on it, it would still only move by 1mm!
It is expensive, but the place where they really get you is in all the fasteners. I just had a bunch of stuff left over from something else, and I didnt want it to go to waste. Therefore, I build audio stuff, haha!