Nordic, I highly suggest you go to a tack store where they sell Eventing Vests and try them all on.
There are many who have the Rodney Powell and the Charles Owen who say they love them and cannot feel the bulk. I ride in my Flex Rider and I have NO ISSUES what-so-ever with how it feels - where others say they are too stiff.
So, YOU need to go and try them all on, because when 1 person says "such n such" vest is too stiff and bulky, and then says "such n such" vest is not, while others will disagree - each opinion is different and each feel and experience differs from person to person - so, go try on all the vests you possibly can, and you decipher yourself as to what vest will work for you.
I see pretty much the majoriy of eventers in my area wearing either Rodney Powell Vests *the norm now* or the Flex Rider like what I have. There are still a few Tipperaries, which is fine - because you need to go with what works best for you.
I have NOT seen this new Aerowear one anywhere.
But again - you need to try on the vests yourself and make your own decision as to what feels best or not.