Insync is dangerous to use across machines.
When a file conflict arises, it does not alert the user.
It just uploads the local copy to Drive, which overrides a conflicting version.
If the user does not notice this and manually resolve the conflict, information will be lost.
This is unacceptable, and much worse than the official Google Drive clients, Dropbox clients.
When a conflict arises, these clients save the file with a new suffix, eg. myfile (2)
Although this is not ideal as it can be overlooked, it is at least one alert.
This issue is very high priority; it is not safe to use insync until you notify the user of conflicts in some way.
I suggest you both save the file with a new suffix like other Drive clients do, but also add other notifications in the Insync client, e.g. a ‘file conflicts’ tab, a popup message option, and also optional email notification.
It would also be helpful if you provided tools for resolving conflicts for common file types, e.g. a diff and merge tool for text files - or at least support to launch third party tools with the right arguments.
Look at how the file synchronizer ‘Unison’ does it. Unison: merging conflicts