That is my thought on all of the ‘cloud’ options. The company writes the software that does the encryption and there is noway to know if there is a backdoor to the system.
I just purchase a Synology 2 disk NAS. It is running at RAID 1 and allows me to access my data from anywhere in world thorough my laptop or my Android phone using HTTPS. True if the house burns down I would lose the data on the disk, but all of the important stuff is on DVD backup anyway and kept in a fireproof safe in the basement.
My data is never going to be out in the clouds.
The "cloud" is being promoted by the same folks that once promoted "Internet push" as the next great technology.
The biggest cloud users on the planet are the ones with a vested interest in the concept (although there are certainly some legit corporate users out there as well - but they are all foolish).
“fireproof safe in the basement.”
Basements, also known to fire departments as “Built In Swimming Pools”. They tend to get filled up by the fire department when they pour water all over your burning house. You might want to also ensure the backups are not only fireproof but water proof as well.