You do not need jack stands with the QuickJack. Current documentation from the company claims QuickJacks are not only designed to be used as jackstands, they are significantly safer because of their more stable footprint. After lifting the car to the desired height, steel tabs are flipped against blocks and the jack lowered until it's supported by the tabs--similar to how a jack stand works.
Regarding a round tube frame, I'd think stability would still be pretty good. The rubber blocks that the frame sits on are pretty hard, but still soft enough that they are a high friction surface. You can also buy pinch weld blocks that have cut outs and might be better for a round tube application. Call or email the company to be sure--they were pretty responsive and easy to deal with when I bought my lift.
https://www.quickjack.com/quickjack-features.html
My biggest criticism is that I'd like a couple more inches of height, so I'm considering adding another or a thicker block. Either that or get a lower creeper (or lose 30 lbs!)