andrew_s wrote: <snip>
The trouble with those examples is that there's only a single adjustment, so the bar height and reach can't be changed independently, so final tinkering is difficult. If you figure the height is correct, but you'd like to try 1 cm less reach, the only way try might be to invert the adjustable stem, and move the clamp quite a lot higher.
My bar height can be changed, but the increments are set by the spacers.
What I am considering is moving the bars up and down (perhaps a bit) in one position, and if it looks as though a bigger move is needed then moving the stem up or down a spacer and then trying adjusting the bars from that position.
If the answer seems to be a shorter or longer stem in one of the spacer positions then I can buy a shorter or longer stem once I have a stable set up.
The adjustable stem seems to make minor tinkering with the set up quicker and more flexible.
The only real benefit of such an adjustable stem would be the scope it gave you to vary the forward reach, not the height of the bars. You already have enough scope to vary the bar height using the existing spacers. Although as you say the increments are set by the spacers, your photograph (copied below) shows that you have a number of different sized spacers, including what look like 5mm and 10mm as well as larger ones. So you can already vary the bar height by increments as small as 5mm by changing the permutation of spacers above and below the stem.
I don't think using an adjustable stem just to vary bar height is practical. It would be pointless using it to fine tune the bar's height by small amounts: 5mm or even 10mm does not make a lot of difference. And using it to make large changes in the bar's height is flawed, because if you rotate the stem through a large angle, you will also make a large change as well to the reach.
It would make sense to use an adjustable stem to determine optimum/preferred stem length, but only if the stem is raised and lowered on the steerer as well using the spacers. So if you thought a shorter stem would be better, you would point the adjustable stem upwards (which would reduce the reach), and then move the bars up and/or down on the steerer to see what (if any) bar height felt right with that reach.
The adjustable stems you have linked to are not really designed for the purpose you want of helping you to identify your optimum/preferred bar height and reach. Look used to sell an adjustable stem (Look Ergostem) which did fulfil that function because it had two pivots in it, not one, but it was never a very popular product.
Given that you also have concerns about your handlebar shape/brake lever position/ability to brake from the drops, you also need to be careful that you do not change too many variables at the same time, because those variables will interact with each other. I would suggest that first you focus on resolving the handlebar shape/brake lever position/ability to brake from the drops, and then consider the reach and bar height.
For example, if you were to decide to replace your compact bars with some which had a more rounded traditional curve, you would probably find that it was easier to grasp the levers from the drops, but at the price of your hands being further forward. That in turn might make you prefer to use a shorter stem than with your current compact bars.