I have a regular Axiom in size L and find it bulky for travel. It has lots of padding and rigid ditchable weight bag shells, which I think is unnecessary when diving tropical destinations in a 3mm wetsuit with 8 lbs of lead. The i3 adds more bulk in the "wrong" place. Basically, the combination of padding and hard plastic makes it so that the BCD doesn't readily fold flat. Instead, you get sort of a pyramid.
This issue isn't unique to the Axiom. Just about any BCD with ditchable weights has this problem, which is why a lot of people opt for travel BCDs or backplate setups.