I have two 27" 4k monitors stacked one above the other. My old stand had problems with the weight of the monitors - it was the joints on the mounts rather than the stand itself - and the monitors kept drooping. I had to tighten the mounts to such a degree that I broke a spanner. Anyway, I've just purchased a Hemudu dual monitor stand and the monitors are staying put without excessive tightening. The only issue I have is that the monitors, being different, do not line up - the upper monitor (Lenovo) is a couple of inches rear of the lower one (Acer Nitro) - and there is no adjustment possible for this. It's not a big issue as that monitor is not a gaming monitor, but it is an irksome one.
After half a day, it's looking good so far.
After half a day, it's looking good so far.