Apart from regular backups, there is some data that I want to archive (e.g., old projects that aren't needed anymore).
I wonder if there is any benefit to using WORM media instead of regular tapes (apart from the inability to accidently overwrite it)? There is no legal/regulatory need for WORM, but I can't find real info whether those tapes are more/less/equally reliable than regular ones.
This is for LTO tapes.
No benefit whatsoever in a technical sense. Some may argue it's "legally safer" (as you write), but I wouldn't vouch for that.
LTO tapes have a write-protect switch. Procedures for if and when a protected tape is reused would make accidental deletion difficult. For example, you might set write protect on an archive you make, and never reuse such a tape for short term backups.
WORM media is supposedly the same, but with tamper detection and overwrite prevention. So more expensive for the compliance feature, but expect similar performance. You could add a couple WORM tapes to your archive to test performance, but I doubt you would get a statistically significant result.
The tape in LTO WORM cartridges and its reliability/longevity is identical to the standard R/W tape. The difference is in the cartridge memory which identifies the tape as WORM. Basically, there's only a legal or logical difference.
If you want to make sure the data is safe you should always have two copies, stored in different buildings/fire sections. Note the vendor specifications and store properly.