Bottom line for me. Some people would run, some people would respect the fact that you were ready to make a commitment, so I'm not going to live my life and make decisions based on what I think people want to hear. I'm just going to be honest. If my honest history makes them run, then we are not compatible. If my honest history doesn't make them run, great. But I'm going to be honest. Of course timing, and how you bring things up matters a great deal. It can come up naturally or it can be awkward.
For me, if I later found out a serious partner of mine had been engaged and had never told me and had no plans to tell me, I would feel lied to and we would not be compatible. Maybe someone else he dates later would prefer not to be told. Great, then they are compatible.
I just don't think it's wrong to want to know these things about someone you are dating, so I'd err on the side of giving people the truth, and letting them decide how important it is to them.