Hydrocide Extreme is a concentrated odor eliminator. The chemistry is similar to Hydrocide, Dynacide, Odorcide, X-cide from various manufacturers. The encapsulating polymer that binds to the odor molecule is more concentrated than most competitors. Hydrocide has no fragrance but hydrocide Extreme has a mild floral fragrance that helps mask urine odors during the time the product is working to eliminate them.
So folks prefer no fragrance so they know for sure if an odor has been eliminated and not merely covered up. They should use Hydrocide. Others like something that makes the work space pleasant while they are working. For them I suggest Hydrocide Extreme.
Hydrocide Extreme (or any liquid) can permanently darken the appearance of nubuck because the fiber will mat down. Again, much the same as other liquids, aniline leather will look darker temporarily when Hydrocide or Hydrocide Extreme is applied, but will return to normal appearance once it is dry.