Yes, clay-tempered swords, such as clay-tempered katanas, are highly regarded and considered to be of excellent quality. Here are some reasons why clay-tempered swords are valued:

1. Differential Hardening: The clay tempering process used in crafting these swords creates a distinct hardness differential along the blade. The hardened edge, known as the ha, is exceptionally sharp and can maintain its edge for a longer time. The softer, more flexible spine, known as the mune, adds durability and resilience to the sword. This combination allows the sword to be both sharp and resistant to breaking or bending under impact.
2. Cutting Ability: Clay-tempered swords are known for their exceptional cutting ability. The sharp edge, combined with the correct geometry and balance of the blade, allows for precise and effective cutting techniques. These swords have been historically used in Japanese martial arts like kenjutsu and iaido, where cutting techniques are emphasized.
3. Visual Aesthetics: Clay-tempered swords often exhibit a visually striking hamon, the temper line along the blade. The unique patterns and variations in the hamon are considered aesthetically pleasing and are often appreciated as works of art. The beauty of the hamon is one of the factors that contribute to the overall value and desirability of clay-tempered swords.
4. Traditional Craftsmanship: Clay tempering is a traditional swordmaking technique that has been practiced for centuries. Swords crafted using this method reflect the skill and craftsmanship of the swordsmith. Clay-tempered swords are often seen as embodying the traditions, techniques, and cultural heritage of the historical swordmaking art.

It is important to note that the quality and performance of any sword, including clay-tempered swords, depend not only on the technique but also on the skill and expertise of the swordsmith. The overall craftsmanship, choice of materials, heat treatment, and attention to detail in forging the blade are all factors that contribute to the final quality of the sword.