The Nea is more of a buzzy vibe, while the Siri is more rumbly. I definitely find the Siri to be more powerful. It just feels like it's vibrating my inner and outer labia with it's rumbly vibrations. I don't get that from the Nea. The Nea feels like it's vibrations are more on the surface. I use to love the Nea, but after getting the Siri, the Nea feels like a weak, cheap and buzzy toy compared to the Siri. I wish I could say I love them both equally for different reasons, but I can't. I have a feeling I'll never love my Nea again now that I've discovered the Siri.
I own the Siri and my partner has the Nea, and I echo what most people are saying here - Siri is stronger and has different/more intuitive controls I think, while the Nea is less strong/more buzzy and has a different shape (and pretty color options, in my opinion, but that's not what ends up mattering when it comes to getting off, haha).