As the title asks, is it safe to use this program? Anything I've found online says you're possibly exposing yourself to risk. But doesn't say anything definitive.
Every VPN you open is subject to monitoring by the service that provides it. The only way you could be certain it isn't is if you set one up on servers you have physical control over. You just have to decide if you trust the providers. I've been using it for years and will continue to do so.
It's not any more dangerous than using my desktop at home. My ISP could set up the same kind of man in the middle attack. Your carrier is in fact watching everything you are sending and doing. That's why the FoxFi app needs to use a VPN to work.