I've never paid for ECBI and in all these years, I've only gotten screwed once in Baltimore. (And that was because it was already a loaded plane/connecting flight.)
I've only ever saved a single seat and it was to let my sister catch up with me and my best friend (who usually does preboarding due to her disability, and I'm her helper.) The three of us travel together, or it's two of us on the same reservation and there's no issue.
I hear a lot of talk about people trolling seat savers, but I've never had it happen to me or even seen an instance of it, and I fly on a fairly regular basis. If someone wants to sit there so badly, they're just going to love flying with the fat, gassy girl who is going to lean over them to talk loudly to her other travel companion for the duration of the flight. No amount of noise-cancelling headphones or eye masks will make me less annoying to someone who is going to be intentionally annoying to me. (Then again, it's a completely hypothetical scenario because whenever someone asks if this seat is taken and I say "I'm sorry, but yes, my companion is coming behind you." The response is, "Oh, okay, thank you!" and they move on. Especially if the boarding position is in the A or early B level, which it almost always is.)