I am a fan of S&W airweight J-frames. I think they are very effective firearms which fill a useful niche. I also shoot them quite a bit and am in favor of shooting them. These light small guns are difficult to shoot well, and I think it is necessary to practice with them if you want to shoot them well.
I had a 642 where the hammer stud broke, but it had more than 5,000 rounds through it, which I think is more than most people would ever shoot out of these guns. Of course, I am never happy about a gun breaking in a way that puts it out of commission, but critical failures can happen with any gun. Despite the problem, I still like J-frames. Broken hammer and trigger studs do seem to be a known failure mode in airweight J-frames, but I don't think this issue is anywhere near frequent enough to be considered common.
Smith replaced my gun with the broken hammer stud, and they sent me a new one in only a few weeks. I believe the studs are not considered replaceable in the aluminum frames. If you have this issue, and there is a long delay for a replacement, you might give Smith a call. The delay may be due to them not having the correct model in stock, and needing to wait until they do the next run. If this is the case, there might be an alternate model which is on hand and which you might like equally well. Also, in my case, I asked if they would be willing to send a 642 no-lock model as a replacement for my broken gun which had a lock, and they were willing to do this. So if there is a very similar gun that you would rather have, you could ask. The worst that could happen is that they say "no."
Since I received the replacement, I have also acquired another airweight J-frame. I have over 3,000 rounds on one and 1500 rounds on the other, and I have not had any further problem. I would not subject one of these guns to thousands and thousands of rounds per year, but they can certainly be shot quite a bit, and I think they should be.