I think Scrying Pool is also an interesting comparison. They function quite differently, but are both good in the same action heavy deck. Scrying Pool is usually stronger, which makes sense since 2P is generally agreed to be a higher cost a than 4 (only a little). I think Herald is probably good in more situations though, not having the commitment of a potion cost. I also think Herald is nice if you have a lot of terminals since it works as a village, and Scrying Pool can not.