Why is Tom Kitten 50p rare?

Could you elaborate on the rarity of the Tom Kitten 50p coin? Is it due to its limited mintage, unique design, or some other factor that contributes to its scarcity? Is it highly sought-after by collectors? How does its rarity compare to other commemorative coins in the UK? And what makes this particular coin stand out amongst the rest? Answers to these questions would help me understand the unique value and intrigue surrounding the Tom Kitten 50p.