Any impact, including a helmet dropped from a moderate height, can compress the inner liner in ways that are not visible from outside. A helmet is designed to absorb one significant impact by sacrificing that inner material, so a helmet involved in a crash should always be replaced, not inspected and reused.
Most manufacturers recommend replacing a handcrafted motorcycle helmets helmet every five to seven years even without a crash, since the internal materials that absorb impact degrade slowly with heat, sweat and UV exposure. The shell can look fine while the protective layer underneath has already lost some of its effectiveness.
A made to order helmet starts long before any material is cut. Measurements are taken, the intended use of the helmet is discussed, and a rider works with the maker to settle on a shell, lining and finish that suit them specifically, rather than picking from fixed stock sizes.
Full face and open face helmets suit different kinds of riding, and the right choice usually comes down to where and how you ride rather than looks alone. A full face helmet covers the chin and jaw, giving more protection in a wider range of impacts, and tends to suit faster roads and longer distances.
A leather trimmed helmet needs a little more attention than a plain shell, but the upkeep is straightforward. Dust and light dirt can be wiped away with a soft, dry cloth, and any marks are best treated with a product made for leather rather than general household cleaners, which can dry the material out over time.
The trade off is scale. A workshop like this will never produce helmets as fast as a large factory, and that is treated as acceptable, since the aim is a considered, well finished helmet rather than the fastest one to market.