I’ve run the free version for the past 3 months and it’s worked great. Works on my android, iPhone and what’s more Lynux!
I can’t attest to longevity. I think they’ve been around for 3 or 4 years. I read here they have around 7 million users.
https://medium.com/@Vanina/dropbox-alternatives-top-5best-cloud-storage-services-2017-a703af7d7796