2012 Sony's AF wasn't great...so that is the biggest compromise I expect. I've never used one but did held it at a store in HK back then. My memory tells me that I felt it was too small, the flat grip, or the lack of a grip to be precise was uncomfortable and felt really dangerous to hold. The whole experience felt cramped and uncomfortable compared to my 5D at the time, which is expected.
This can be easily fixed with after-market grip though but the AF is the older contrast detect, not phase detect so you need to be aware of where the focus point is hitting. On the 5D2 and 5D3, when using outer points which are contrast detect, I make sure the focus points hits between 2 distinct things, like between the white shirt to the jacket collar, things like that.