The learning experience
Calligraphy is decorative handwriting and lettering. There is no "toy" it is just a skill you can learn. It's similar to drawing/painting to relax you and keep you focused.
My initial thoughts on calligraphy are that I thought it was really pretty, and I wanted to learn the skill.
Review: I thought it was a lot of fun to learn, and very relaxing. Skill wise, I would give it a medium to hard. The challenge is what makes some of the fun. I don't necessarily think you need prior knowledge to learn how to. Just the use of a pen, I used a picture as a reference and just copied it. There are a lot of great you tube tutorials out there. my Recommendation for this would probably be, formal thank you notes.
After learning this skill, I will/would probably just show off my new handwriting and write letters. Maybe invest in some things that are made for calligraphy.