Pros: Fun for the kid
Cons: Noise can be annoying depending on your mood.
My husband, my 18 month old and I were out shopping during the Christmas season and happened in a very dangerous store called All Wound Up (dangerous to the pocketbook since they have a lot of the toys out to play with). Well, our son noticed this toy on the floor and started pulling it around the store. He would stop at other toy displays, drop the string to the toy, play with the other toy for a minute, pick the string back up and walk to the next interesting display (instead of going from one toy to the next like most kids that age)! We decided that since it was only $10 and he didn't have any pull toys yet, that we could splurge on it for him. Luckily we did. As we were walking out of the store with the new boxed toy, he was walking out with the display model! I pulled the toy out of the box quickly and switched the toys on him (I wanted one with fresh batteries since they are not replaceable). We proceeded with the rest of our shopping trip with quacking toy in tow and funny looks from other people, until they figured out where the noise was coming from! :)
He's had the toy for quite a few months now and still plays with it often, at least whenever he notices it amongst the rest of the toys in his collection (I really need to start rotating them)!
The material holds up really well. The toy tips on its side frequently (a slight annoyance) and there are no scratches resulting from being dragged across the floor on its side.
The quacking can get extremely annoying ... there are times I can't wait until the enclosed batteries where out! But it really is a cute sound. Kind of like a song you really like on the radio and learn to detest because it's played too many times within too short a period of time.
Others have mentioned the length of the string. The string on our toy is a bit too short (I have a tall kid) causing him to make the ducks tip to the side quite often. I don't believe it to be a choking or strangulation hazard at all, since there is nothing on the pull end of the string to get caught on anything. As with anything, you need to careful, but I don't believe there is any honest danger in this toy.
With my kids being 2 years apart (the youngest not due until August), I think I'll be hearing quacking noises for a few years to come!