The Pro version has a Panavice(sp?) suction vice to hold the unit to your mounting surface-like your countertop and stays consistent in your angle reference while the APEX's suction cups raise up aas you use the device. This means that you have to re-calibrate the angle cube to the blade table each time you change stones because the suction cups hav raised a little bit. Not a big deal but it bothered me.
The blade table on the Pro is wider so I find it easier to hold the knife steady while sharpening.
The Pro is made from different plastic and is heavier and sturdier....not that the APEX ix flimsy, just a bit less sturdy as it's lighter.
Having said that, there have been times when I clean up only to find that the base of the Pro is no longer stuck to the countertop but my reference angle never changed.... Oh yeah ,I use light strokes.
The APEX is a great tool and it was the first EP I bought but I'm happy that I got the Pro with the scissor attachment over two years ago.
+1 on a Nubatama set