The Samsung Galaxy S8 and S8+ already has a decent-sized battery, but it is not he largest available. It seems that Samsung has worked out that there is a market for an external battery pack.
There are already shedloads of battery packs out there so it is odd that Samsung thought it worthwhile to compete. Particularly if they catch fire you can always blame your partner. However this one does have certain advantages.
It supports fast charging which means that you will not be hanging around waiting like you would for the standard 2A output,. It uses a USB-C port to connect to devices, although there will be a USB-C to micro USB converter should you want to use it with a non USB-C device. The battery itself will charge via micro USB so there is no need for an extra USB-C cable or charger.
The battery pack is decently priced at $60 and it can be bought directly from Samsung's website.