It's the drive side crank arm. It comes out very straight from the BB, with no bend and the arm is very square. Net effect is that you need to adjust your front mech so it only shifts as far as 0.5 mm from the arm, which iny set up, is not enough to shift up crisply. I have remedied this by spacing the chainrings inboard using a mm GXP spacer..
Works fine, but not ideal, and I needed to do this on both my bikes using them (both 11 speed Shimano). Not a problem if using a single ring of course, and you may really like the chunky styling (which I did until it hit my mech!).
Up close the Senicx just looks a higher quality product all round, in pretty much every detail. The forging, the finishing, and functionally. The chainrings are similar but even they look a little better on the Senicx. It only costs marginally more and IMO money well spent.
Note the Senicx is the same crank arm set up as you get in the GEOID PM500 (I have one of these too) and in that thread people are saying the cranks are better then the OG Magene ones.