Be careful, encryption in 4.1 is not compatible with encryption in 3.5. If you update it will erase everything.
Also, bluetooth in 4.1 is broken and I’m not sure if a fix is coming. I’m thinking about going back to 3.5 myself.
Encryption in 4.1 is compatible with 3.5, there should not be any issue. However encryption in iodéOS 4.x and iodéOS 3.x is not compatible with encryption in 2.x: factory reset required to upgrade from 2.x.