For Commander, I think they are both at the very least solid cards but become much better the higher-power Commander you like to play
Here are some places I like this: Spellslinger - Alongside triggers like Guttersnipe or Talrand, Sky Summoner in Izzet, with Jeskai or Boros with Young Pyromancer or Monastery Mentor
What are the key cards in my opponents deck
Notably, Neriv doubles all damage, not just combat damage, so you can do some disgusting nonsense with cards like Fanatic of Mogis and Overlord of the Boilerbilges
Spymasters Vault Spymaster's Vault has similar deck building requirements to Castle Locthwain (read: almost none), so suffice to say itll enter untapped 90% of the time
In some rare cases, a nonartifact card put onto the battlefield this way will get two +1/+1 counters because some other effect (like that of Mycosynth Lattice) makes it an artifact on the battlefield