FYI the desktop version is completely free to use and relies on the desktop sync apps of the various cloud storage providers, the android version does cost about £8 but I believe it hooks directly into the providers' APIs so you don't need to install their apps. The free experience was good enough for me that I was willing to fork out for the app, much cheaper in the long run than paying a monthly sub!

It's awesome! I'm running this since years without any problems.

True, the safest data is the one that never goes online! But realistically it's a tradeoff between risk and convenience - you can self host your own off-site backup but it's a lot less effort to use a cloud storage provider, both are much less risky than having no backup and losing everything if your drive fails or your house burns down. At least this way I need the provider or my PC to be compromised and the encryption to be broken. TBH if quantum computing suddenly starts breaking encryption everywhere then we'll all have bigger problems like the collapse of every bank in the world!