I know they are a scam when it comes to their claims of extended battery life. However, the product itself appears to be legit in terms of being a boost converter if that's actually what you need (in most cases you don't, but I guess running certain devices that need exactly 1.5V and can't take the lower ~1.2V from rechargeable cells would make this a legitimate use-case for it).
Stay away, they are a well known and debunked scam.
https://www.indiegogo.com/projects/batteroo-reboost-make-rec...
https://en.wikipedia.org/wiki/Batteroo_Boost
https://www.eevblog.com/forum/blog/eevblog-751-how-to-debunk...
Don't miss this one!
https://www.youtube.com/watch?v=OU08zwBH-wo