I have both of these.
The Jopen Vr6 felt a little like a clamp to me, as the clitoral arm doesn't have much flexibility. Also, I have to be REALLY in the mood for this toy in order to insert it comfortably, due to the curve of the shaft. That said, the Vr6 is one of the most powerful vibrators I own. Both the shaft and the clitoral arm are EXTREMELY powerful. It's a lovely, rumbly type of vibration, too. Very impressive vibrations.
The Vr3 is more comfortable for me to use, but the vibrations in that one just aren't as great. The shaft is really powerful and rumbly, but the clitoral arm is super buzzy. Personally, I don't get any pleasure out of the clit arm, as it's just too buzzy for me.
My favorite Jopen so far is the Vr.6.5