From what I've seen online, the 5 is trivially larger (like 1mm each way).

What drives me to the 4a is the brighter screen, slightly lighter, and plastic. So when I drop it (not if), it'll bounce better.

Also, they're cheap as hell from Walmart of all places, about $100, lol. So I can afford 2 or 3 of them for the cost of a newer phone that has performance and features I really don't care about.