I've been riding with the porteur rack for about a week and a half now, and though I've found some definite faults, I'm very pleased overall.
One of the big issues is vibration. Since the rack is above and forward of the hub, any bumps in the road get transferred straight to the rack, and the movement is actually slightly increased on the front end of the rack. My most common cargo is muffins carried in a large (2'x3') plastic container. Any bumps rattle the container, shuffling the cargo around. If I want to keep making these deliveries by bike, I cannot have any casualties. Possible solutions include running the front tire at a lower pressure, or putting a towel in the containter to absorb some of the vibration.
The second issue is height. The rack ended up about three inches above the fender. In many cases, this puts any cargo I carry above the line of my handlebar mounted headlight. Even if the rack was moved down, any larger cargo would still get in the way. None of my bikes have any sort of mid fork braze on, but there has to be some way to get a light mounted either on the underside of the rack, or on to the fork.
Managing the bike is also a bit of an adjustment. Especially when the load is very wide, the handling becomes almost boat like. Any wiggling when starting from a dead stop can throw your balance off. It's not unpleasant, just different.
Those issues aside, I've been very happy with how the rack is performing. It's been solid, no creaks or clanks, and has handled everything that I throw at it. No paint as of yet, that will have to wait until we get warmer weather.