Hello, you can save your progress without issue on either versions (Steam or Android).
The "Save to Disk" option is an additional, separate save option that allows to save anywhere on the drive on PC/macOS, it seems to sometimes malfunction on mobile.
As for sales on the Play Store, they are a bit cumbersome to set up as I have to manually set a new price for each country where the game is available (100+), so I don't do them often (maybe once a year).