I've worn a 2xu tri-suit for a 200km audax before. While there are arguably aero benefits to it, but some downsides as well:
1) most tri-suits have no, or very small, back pockets which don't hold much.
2) the padding is thinner and designed to be comfortable during the run leg... which means less comfort on the bike leg.
3) using the toilet is trickier than bibshorts.