I consider TAILS safe enough for me. Always check and verify you downloaded a genuine version of it and other cryptocurrency related software. This verification step should never be skipped. Be aware that TAILS is agnostic, forgets everything you saved, unless you have a persistent storage partition setup (which is usually or should be encrypted; don't forget or loose the decryption passphrase!).

Don't rely on a single USB flash device, be it with TAILS or some other encrypted container or other valuable data on it, as such devices can fail. Cheap flash storage is sometimes of questionable quality. No backups, no mercy!