Generally phones newer than 2016 support Android 6.

Please know that Clearing the Cache will NOT remove any photos from your device or computer. That action would require a deletion. What WILL happen is, the Data files that are stored temporarily in your device's Memory, that will be the only thing deleted once the cache is cleared. This system ensures that your device isn't bogged down by so much storage that it can't tackle anything new.

Clickfree has the capability of knowing what it has previously backed up, so you won't have to worry about running into duplicates each time you use your Clickfree device. 

Every time you are using your Clickfree device it will automatically resume your previous backup if you have not been able to do a complete full backup of everything on your device.