What Pat said.
Personally, I use a spreadsheet for my logs which is backed up regularly. I get to decide what fields I want to include (or not) and am able to analyse the date far better than an app will allow.
My data isn't able to be seen by anyone but me unless the CAA come knocking on my door. (by the way, I have two log books. One for me and one for the CAA if they ever request my logs. Not that I want to hide anything: The CAA require far less detail than is included in my main logs)