Liver is generally a great source of nutrients and very rich in Vitamin A.
Risks
Over time, excess vitamin A can lead to a serious toxicity called hypervitaminosis A, which leads to bone deformity and even fusion of elements of the spine.
Suggestions
Liver can be given to cats in moderation, but it should not be a regular part of their diet due to the risk of vitamin A toxicity.
Note: even if labeled as safe, any food can potentially cause allergies. When introducing a new food, please feed a small amount and observe your cat for any allergic reactions.