I agree with what Stormy already mentioned.
I would choose the Jopens over the G4 P2 because of the finicky style of the G4 P2 clit arm. However, if you like rumbly vibes, the G4's are really awesome, the only problem being most are big. Oh, one more difference between the brands, the Jopens have constant vibrations and the G4's do have some pattern options, if that is important to you. But, the Jopen Vr12 I have has wonderful, rumbly vibrations, so I expect, at least with vibrations, you will be fine with either brand.
So, it comes down to the design. I agree, it's difficult to get a clit arm that works for you and if you know what does, then it's easier. Do you have any rabbit style vibes that work for you? I assume that you chose the style of the Vr4.5 because you thought it would work for you. I think the big difference between the two Jopens is that the Vr9 allows firm pressure on the G-spot and the Vr4.5 is much more flexible and perhaps may not work as well for that. Certainly, you would have more maneuverability with the Vr9 and you can always use a separate vibe, your fingers, or someone's tongue on your clit. So I think the Vr9 is the safest bet out them all.
I hope you get one, hopefully enjoy it and then let us know you thought of your choice!