Several good points mentioned. I learned form a very experienced instructor. He was a bugger about setting the mechanical trims and still is. If it's off even just a little he had me correct mechanically first. It should be added that the Tx settings are all in the neutral position and the servo horns are checked to be neutral with the Tx. as well, before adjusting mechanically. These are things we all learn usually after we have been flying for a while, unfortunately. Then you check the mechanical settings to get the movable surfaces perfectly neutral. The benefit to you is that you now have the full range of the trim settings on the radio to work with. Nothing worse than begin at a full trim only to find that you still have a problem and need more trim.

One other thing. Hard to imagine how your airplane gets seriously out of trim once adjusted for hands off level flight, unless someone is knob twitling with your Tx. It happens