Well I know that my posture is changing things - and once I’ve documented and skull mapped over a long period of time I’ll know for sure that it’s working with “proof” beyond photos which could be off... but lately it’s hard to say from even my own pics that’s all imaginary and in my head - it seems like things changed! It’s just a log habit to create, improve, and get better at :) 

Most appliances only apply force to the teeth and provide limited actual skeletal expansion, especially in adults. What they are mostly doing is tilting the teeth outwards, meaning that your teeth are being tipped or flared. So even if you are able to turn the screw consistently, it doesn't mean that you are making much actual skeletal progress.

From my time lurking around different communities like this one what I have seen is that people who choose to use appliances usually end up not very pleased with their results. Instead of reaching a higher level of health, they end up somewhat worse off physically and mentally for some reason - that's just what I have noticed and I don't know exactly why.

Now I can't say for sure about your case, and I don't have all the answers, but I think that a good rule of thumb is that if you want natural results then you need to use natural methods. When you use natural methods and natural posture your whole body changes in order to accommodate you. From the top of your skull to the tips of your toes your body your body will experience changes in skeleton, muscle, nerves, and connective tissue in response to your new habits. On the other hand when you use an appliance you keep everything else the same and rely on the appliance itself to push your teeth around somewhat.

The hardest part about all of this is trusting that results will happen because as you said, there's no quantifiable measure like being able to turn a screw to see that things are changing. My advice for that is to take progress pictures every few months and also to read as many success stories as you can get your hands on so that you can see that this stuff actually does work. I have actually collected a few success stories and will see about getting them posted to the proper thread soon.

If you can fit your tongue onto your palate then my advice would be to try things the natural way first to see if you can make changes yourself. If you do go ahead with the appliance just make sure you have a realistic idea of what doctors and appliances are actually able to do - don't expect the world of them.