In what manner? I honestly can't fault them - great coverage, absolutely rock solid, only ~50g heavier than chromoplastics, easy to fit.. I actually can't think of a bad point, apart from the price.
They rub the calipers on the Defy 0 according to my LBS who were fitting some for a customer when I was there talking about my Speedshield guards.
Coverage and robustness of them is brilliant but I'm getting a bit of rattling. I reckon it's the rear guard buzzing against the underside of the caliper. I might try and find a way to isolate it and see if that helps.
I've previously used sticky back velcro on my frame to combat rubbing from things like frame mounted pumps, mudguards and even a small part where the bike rack at work touches my frame (although slightly too late as I already had a mark

).
I've got a disc braked Defy Advanced 1 and I'd like to fit some mudguards to it for the winter, but unfortunately it hasn't got specific mounts, has anyone fitted mudguards to one?
I was looking at Crud RoadRacer Mk2 but can't seem to find any info about fitting them to a bike with disc brakes.
Giant now do a set of guards speicifically for your bike. Speedshield Universal.
They work much better than cruds aswell
The new Giant range of Speedshield guards have some designed specifically for the
Defy Advanced (Discs) and another set designed for the
normal Defy (Rims). I know because my LBS got their delivery in, I went to pickup a pair and they only had the Defy Advanced ones. They had to order me some normal Defy ones in, there was a conversation they had with their Giant rep who said the Advanced guards would not fit a normal Defy properly.
I have a normal Defy 1 and tried a set of them out, they're only slightly better than the 'old Giant Fenders' they replaced, which were horrific for noise, flexibility and banging the frame. I have previously used Crud's and would say noise from the Speedshields is the same, although they do have better coverage and clearance for 25mm.
My SKS Raceblade Longs are a much better fitting guard, with less flex, much less noise and similar coverage. I can't rate them enough! Although I'm unsure if they would be compatible with the Advanced as it doesn't have mountpoints and I don't think it has bridge points/holes?
Totally down to you, but in my opinion Giant's guards are terrible, they had the perfect opportunity to 'reinvent' them and still missed the mark. SKS deserve your money and in the long term you have a better guard.