Anyone used one of these Velo Orange Cigne Stems? I'm wondering if they would be safe for an aluminum steerer tube.

https://velo-orange.com/products/cigne-stem

This isn't an engineering answer, but I feel like I have heard about way too many failed aluminum steerer tubes. The way this stem works by pinching just on the bottom, along with the odd leverage suggests disaster. I would absolutely avoid that stem on aluminum steerers unless the manufacturer of the stem says that is approved. (And then I still wouldn't.)

You could call Velo Orange and ask. I’m using one but on steel.

I am raising bars due to age and arthritis but this 145mm stem rise with a aluminum steerer tube adds a lot of loading and would make me very nervous over time. While a steel or titanium tube can take an infinite number of loads under their fatigue limit aluminum can not, it does not have a limit at which it starts fatiguing, every even small loading can eventually add up to a failure. Fortunately aluminum frame designers know this and build frame with this in mind.

Aluminum can be very strong, but it needs volume to accomplish that. Standardized steerer tube expander plugs and headset diameters mean that aluminum steerers never receive more material than steel steerers, which makes them much weaker. So the question is: Are 1 1/8" steel steerers so massively overbuilt that cutting the tensile strength in half by going to aluminum has no effect?