Your opinion about Heartsteel

I started playing Shen mid because i saw it on youtube and i'm having a lot of fun. I usually go for one of the Bami's Cinder items and Deadman's Plate, but i've seen some players building Heartsteel.

I would like your help to understand the benefits of the item and if it would be good on midlane.

(Sorry about the english, not used to write or speak, but i can understand it perfectly. I'm brazilian, so if you're like me, help me in Brazilian Portuguese)