I have only written 2 articles for Constant Content, I just got too busy with other things. One of the articles sold within a few weeks, the other never did. So yes, you can make money, but it is so uncertain as to what your 'hit rate' will be that it might not be worth it. The articles that never get sold are basically just 'sitting around' and you can't use them for anything else.
Basically, in my very limited experience so far, yes it is a legitimate site and you can make some money off it, but if you have a low 'hit rate' for articles getting sold then you will have put in a lot of work on articles that will not make you a cent. I wouldn't say that Constant Content is 'better' or 'worse' than other writing sites like Hubpages, Associated Content, etc - it is just different and has a different set of pros and cons. One thing I *DO* like is that it has a stringent editorial process, meaning that the site gets known by buyers as a high-quality site. (Strangely enough, I've heard other writers complain, yes complain, about the editorial process - it's true that it can be a little slow at times but I would say that any writer with a reasonable grasp of grammar should be able to have their articles pass the editorial process).
You could always try testing it out by writing a few articles and see how they do. Some people find that their writing tends to naturally 'suit' a certain site over another site. My guess is that for me, Hubpages may be the better bet in the long term.