Let's discuss this offline and loop back when we converge. I don't want the exchanges to be viewed as bickering or detracting from the overall topic. But it is something important (to me at least) to discuss.Sorry I do not quiet agree.
Neutrally buyont has nothing to do with a specific trim in first place.
An object is described by the location of its centre of mass and the orientation (i.e. three angles) for a given imaginary line between the centre of mass and a reference point inside the "object" with respect to the outside coordinates.
Neutrally buyont means: no up and down movements (we ignore for a moment rhe fluctuations due to breathing as they always are present) in the water column and NO internal force used to stabilize the depth.
That is independent of the objects orientation! If you want you can stand up and be fully neutral.
Now you are talking about horizontal trim. That means you want to achieve an objects orientation neutrally horizontal as well, that means without using fins and/or hands to maintan that. Fine that is a good skill to master, especially because it helps(!) to be easier neutral if you stop kicking, because you want to observe something. And it helps to not disturb or damage the underwater world. I agree. It should be taught that this is a goal and how to achieve it. I agree again. If you need additional force to maintain the desired trim position, then your trim is unstable, not neccessarily the buyoncy. And because of using force to maintain the trim position, it has secondary impact on your buyoncy as well, as you start using some force that goes up or down as well automatically.
But its physically wrong to say one is only neutrally buyont if one has a horizontal trim position. If we want to teach this in a good way, we should be precise in the physical definition as well.