Mint is a relative of Catnip and so it's perfectly healthy for them to eat. It's pretty healthy for us people too especially when in it's chocolate chip ice cream.
My cat's have been eating my Ikea decorations which I thought were fake but must be chemical treated real sticks and branches. It came with the apartment, I didn't buy but they manage to fit in. I chase them away from it when I catch them but I can't be home all the time. I was trying to grow some cat grass but my bigger cat would pull them out before they really got to a healthy size and then he would dig the dirt all over the floor.
https://petdynamics.org/2013/04/18/the-benefits-of-cat-grass/
I was passing by the local plant shop I go by daily by all the little street food vendors. I took a quick scan but nothing from 
I got home and put it on the floor and they cats did a take few bites but mostly they smelled it and stuck their noses right in to the leaves. They must have been really missing fresh plants in my home. I have trees outside and keep the windows open so they get fresh but it'snot the same. Afterwards they went back to sleep.
I was interested in why Mint was good for cats. I got online and Today I Learned that Mint is related Catnip so the smells, at least to their highly tuned noses, are similar. I have never smelled fresh Catnip so I can't say. The essential oils in Mint will make your cat sick so don't let them eat candies or toothpaste. Cats also shouldn't indulge in the fresh mint leaves as too much can give them upset stomachs which equals barfing and having to clean it up.
I will probably eat a bunch of it too. I like mint, it's great excuse to make Mojito's. Though it does have a lot health benefits for us human's too. Let's take a quick peak at why you should eat it too.
(image http://www.twopinkcanaries.com/health-benefits-of-mint-leaves/)
It's also used in several magic potions. Wicca is loves the stuff
➊ Break Magic Spells
➋ Keep Evil Spirits Away
➌ Reverse the effects of some potions and poisons
It probably comes down to it's medicinal benefits.