Short answer: Time Machine is better on a drive at home. Copy Shelter is better everywhere else, and it tells you whether the backup can actually be read.
Running both covers more than either does alone. Copy Shelter writes only where you point it, and it warns you if you point it at Time Machine's disk.
| Copy Shelter | Time Machine | |
|---|---|---|
| Space needed | About what your files take, less what repeats | Refuses a disk it thinks is too small, judged by whole disk size, not by what is on it |
| Where backups can go | Any folder: a drive, a NAS, or a cloud folder you already pay for | A disk it formats, or a supported network share |
| More than one copy | As many as you like, each checked separately | Several disks, used in rotation |
| Knowing the backup worked | Reads the backup back on a schedule and says what it found | Verifies network backups occasionally and tells you little |
| Encryption | Always, and not a setting: there is no way to make an unencrypted one | A tick box when you choose the disk, with a password you set then |
| Restoring a whole Mac | Restores your files onto a fresh macOS | Migration Assistant restores from it directly during setup |
| Cost | Free for one location, paid for more | Included with macOS |
| Local snapshots | None: it backs up to somewhere else | Keeps hourly snapshots on the Mac itself, useful before a backup runs |
| If the maker disappears | Documented format, readable by a free single-file tool | Apple is not going anywhere |
Three rows above, and they matter. Migration Assistant restoring a whole Mac during setup is the smoothest recovery on any platform, and Copy Shelter does not have an equivalent: it puts your files back on top of a macOS you installed from Apple. Time Machine is free with the operating system. And its local snapshots catch the mistake you made ten minutes ago, before any backup ran at all.
Time Machine wants a disk. If the storage you have is a folder inside iCloud Drive, Dropbox, Proton Drive or Google Drive, that space is not available to it at all, and that space is usually already paid for. Copy Shelter writes to any folder your Mac can write to.
The larger difference is that Copy Shelter reads the backup back. Every piece is checked against the hash it was stored under as it is written and whenever you ask, a sample is checked every week, and a piece that has been deleted is reported as missing. Time Machine verifies network backups occasionally, and tells you very little either way.
Running both is a reasonable thing to do, and it is what we would suggest. Time Machine on a drive at home, for the local snapshots and the setup-time restore. Copy Shelter to a cloud folder or a second drive, for the off-site copy, and it checks that copy.
They do not interfere. Copy Shelter writes only to the folder you choose, and neither one knows the other is there.
No, and neither can any other backup tool that is not Time Machine. Apple seals the system volume, so macOS itself always comes back from Apple. What Copy Shelter restores is everything that was yours, put back on top of a fresh install.
You can, technically, since Copy Shelter writes to any folder. It is a poor idea: one disk failure would take both backups. Use a different disk, or a cloud folder.
Only if you tick the box when you choose the disk, and the password you set then is what protects it. Copy Shelter has no such box: everything is encrypted before it leaves your Mac, and there is no way to turn that off.
If you have a spare drive that lives at home and you want one thing set up and forgotten, Time Machine is a good answer and it is free. If your storage is a cloud folder, or you want to know whether the backup is readable, Copy Shelter. Most people are better off with both.