Quick answer: Diffuser: it spreads airflow through prongs and vents, drying curls or waves with low-velocity, indirect air instead of a narrow jet. That preserves clump formation, reduces blow-apart frizz, and lets you “cup” sections for 20–60 seconds at a time. A concentrator smooths and directs; it cannot cradle texture evenly. What a diffuser does…
Boar, nylon and mixed round brushes behave differently under heat and tension. The right choice depends on grip, finish, density and control.
Hair dryer wattage tells you power draw, not finish quality. The right dryer balances heat, airflow, nozzle control and hair type.
Ionic and ceramic do different jobs. One affects water and finish, the other affects how heat is spread and delivered.