What was the deal with the watch? -spoilers-

[Balls]

So after you get your arm chopped off and re-attached, you have a wrist watch, which Zoe says is a codex. The watch doesn't come into play at all during the campaign except for on the ship during the flashback moment where we find out its used for tracking Evelin.
And when redfield calls you at the end, he communicates through the watch.

What was the point of it? Why did the Baker's put it on your arm if it's Umbrella tech that can be used against Evelyn? And how does Zoe know what it is?

[Balls]

Ah I suppose that makes sense. I picked Mia to give the serum to. Does chosing Zoe give more info into her back story? Her motivations were never really fleshed out from what I remember.. other than she's not a psychopath like the rest of the family.