That 2 handed version is something i've been suggesting for years, it doesn't get any better than that.
I tried 1 arm extensions in the 70s, didn't like them much both because they put more pressure on the elbows and because the extra balance required didn't make it as good, to me.
But after reading this today i decided to try them again in this afternoon's workout. I did 1 arms fully bent over, using an overhead cable. What i'd suggest, to get the most out of 1 arms:
-If you do them seated with DBs, alot of people find these eventually hurt the elbows due to the angle of the resistance, in which case modify the ROM a little to avoid that. Martinez for example, lowers his elbow more and says this keeps the pressure off the elbows.
-Use cables - you not only get the constant tension, you also have a much larger range of possible angles to try, PLUS the resistance comes at you in different ways from free weights-it's easier to transfer the pressure to the muscle and off the elbows.