Even if it is not the cloud, backing it up to a separate drive (at least once) is well worth doing.Yes I agree about the backing up. Have never really liked the idea of cloud stuff before but this might have changed my mind.
I learned my lesson when my HDD crashed a few years back - lost 3 years of photos including some of family and friends who are no longer with us. Nothing I can now do to get them back.
With regards to Subsurface, it was started by the one of the principal authors of Linux (Linus Torvalds) and is open source. If you are worried about cloud security, I have to ask why anyone would want to hack dive logs?