I am not in my 40s, but my mom is in her early 50s, and she met her now husband on eHarmony about 4 years ago. She says she can't imagine meeting anyone more compatible with her, and it's the happiest I've seen her in a long time. They grew up one town apart their whole lives, but they still probably would have never have found each other without the help of that site, and she still glows when she talks about it. She has a few other friends - some of which are in their 40s, one is even in her 60s - who have met their spouses or partners on eHarmony, as well.
I only have an outsider's perspective, but it seems legit to me.