There is a diagram in that link, for some reason the graphic wouldn't paste.

Yeah, I tell you, I've been trying to understand the limitations of carbon parts for some time. Hard to cut past all the emotion and deflection sometimes.

Please, you already called used the word "ignorance", so please stop sounding wounded.

Yes, you don't understand how the clamp on a steerer extender works - and even when I explained to you the difference you persist. If my description isn't enough for those gifted in high school physics to understand, what would?

It's a bad idea, and the fact that you can't understand why and have no experience with either carbon OR extenders doesn't make it okay for you to try and convince innocent third parties to do something super dumb because you think it is all simple.

I think the nuance is most stems have a complete split seam on the back where the two pinch bolts apply clamping pressure. It's a split cylinder and, as long as the two pinch bolts are torqued to similar values, the clamping pressure should be pretty consistent on the steer tube along the length of that split cylinder.

Most stem risers are not split along the entire rear-facing edge like stems are. Most have two pinch bolts, but there's usually solid material just a short bit above the upper pinch bolt. This means the stem riser will not be clamped on the steer tube uniformly. It slides over the steer tube as a split cylinder, but the lower pinch bolt compresses that split cylinder more than the upper pinch bolt can (because the cylinder is solid, and not split, above the upper pinch bolt). So it ends up looking more like a split cone than a split cylinder. I think that's what Kontact was saying earlier -- this uneven clamping, or this "split cone" hardware if you will, will end up digging that lower edge into a soft carbon steer tube (even if it's on a small scale and not outwardly visible).

Interesting. Very true that they all turn solid at the top. I will say the ones I've used are split past the top of max insertion point of the tube. There is a mechanical lip that prevents over insertion. Is that enough to equalize the pressure? Hard to say, especially with the low torque points.

Yeah, I saw the diagram and was just letting you know that I found no problem with using them if they illustrate the point. I think there's more to it than that, but the more I consider your points and the more I think about it myself, the more I realize it's just too far above my head and I don't care to delve further into the subject. Sounds like the OP made their decision no matter who wins this debate.

The Satori has a cylindrical not the split style, a much better look than the Delta. The delta is split clamp.
I don't have a picture of the Delta

At some level, anything except for a full split cylinder should, at least in theory, prevent even clamping pressure. Is it enough to cause harm in practice? I certainly cannot answer that.

I have, use, and enjoy a stem riser on one of my mountain bikes. It's a cheap no-name from Amazon and it's worked fine. It's on an aluminum steer tube, though, and I don't think there are generally any concerns with such a setup. I use it as a "soft roader" bike only, and don't subject the bar or stem or riser to any loads higher than what I'd consider "moderate" trail type riding.

Nobody here is being hostile or condescending. You have been told by a few people in this thread that you are wrong, yet you double down. As Kontact said, it is not OK to try and convince people that warnings on products should be ignored. That is whether it is bike stem extenders or ladders.

Love those Monte Cristo Whites.

The origin 8 stem I use looks a lot like the one you posted.

Listen to the warnings but ask questions. I learned a few things so worthwhile discussion. What I said about the leverage isn't wrong. High school math as some non-hostile person pointed out.

I think this thread has run its course, there is enough information here for people to make their own choice.

Have a nice day. Need to go adjust the headset on my stem extended bike, it needs a tweak after I replaced the front fork.

Learning is always good.

At the end of the day, it's not whether the odds are in your favor. It's what are the consequences of being wrong?

This type of clamp is never permissable on carbon steerers, even on stems.