General practice with the single action could be useful, to get used to actually spraying, and becoming familiar with grip, and keeping the 'brush 'square on' to the surface being sprayed, rather than 'twisting the wrist', which causes 'feathering' and possibly an uneven finish.
However, the sooner you become accustomed to the 'feel' of the double-action, the sooner you can use it 'live'. It doesn't take long to 'get the hang' of the trigger pressure, spray pattern etc, and the double will allow much more precise control and a smoother spraying action, resulting in a good, clean, even finish.
Get some paper (copier paper or decorator's 'lining' paper, on long rolls, is ideal), and some kiddies liquid water colour paints, and practice the spraying actions, especially fine-line work, when you can then sign your name and draw straight, curved and looped fine lines.
Progress to curved surfaces, using disposable coffee cups, and then repeat this practice with the chosen paint types.
Also, become accustomed to part-stripping and cleaning the 'brush after each use, ensuring any paint is thoroughly rinsed out, and the needle and nozzle are clean and free from any dried pigment.
Keep the 'brush clean and paint/pigment free at all times, and it should last you many years.