They are fine to use as long as you appreciate their risks and drawbacks. The two main ones are malicious similar addresses as described above (although an attacker can do that for any address, not just vanity addresses) and the fact they encourage address reuse.
To add to this, and being a privacy freak, I can't conceive the idea of having a unique address that could be easily tied to one person/user. I'm fully aware that all addresses that are posted in here are searchable in some forums tools (such as Ninjastic[1]) but having a unique addresses makes things worse.
Also, by using samr7 excellent vanity address generator[2][3], you'll end up with Pay-to-Public-Key-Hash (P2PKH) addresses (starting with "1...") which will incur in higher fees whenever someone (or yourself) interacts with that address regarding miner fees. If one still wants to generate addresses that support P2PKH, P2SH and BECH32 I guess that they could always use Jean_Luc (also excellent) vanity address generator[4][5].
[1]
https://ninjastic.space/addresses[2]
https://bitcointalk.org/index.php?topic=25804.0[3]
https://github.com/samr7/vanitygen[4]
https://bitcointalk.org/index.php?topic=5112311.0[5]
https://github.com/JeanLucPons/VanitySearch