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.