They're all fairly similar - all made with the Power Bullet technology, so they all vibrate in a similar way. Some are more or less powerful than others, and then there are the different styles / shapes / configurations - so that is a little variety.

But they are all fairly similar. (In my experience, anyway.)

I think they're different enough that some will work for one person but not for others because of anatomy.

They differ somewhat from each other. The 6.5 is one of the strongest ones. If you're looking for just the same strength try the 6 or 4.5. Not sure what your anatomy is like, but those are the strongest ones.

I have the 6.5 and then 5.5 and I love them both and they are different!

I just bought the 5.5 for my wife - yet to use it as she is away!!

One thing i noticed in my 3 weeks of research is how they bend! - I think it was the vr3 shaft is really flexible and i noticed that in some reviews, so when i picked up the 5.5 and it was SOLID and doesnt flex i was stunned and thought... "why doesnt someone do a really good Jopen comparison for people!!!!"
On the other hand i do love the non bendyness as someone mentioned that if it bends lots u cant put enough pressue on the gspot as it just bends away!

I have tried a great number of them and they are all different, hence why they are all designed different. It depends on your anatomy and what you like to what actually works. I would recommend the Vr3 for your next Jopen.

the shapes are different didnt effects