Yes, I think Luminosity does help ADHD - although you need the patience and determination to stick with it.
I would recommend giving the Luminosity free trial a go - you don't have to spend money if you don't think it's worth it. And even if you do sign up, it's $10/month and you can cancel at any time as I understand it.
So does lumosity work for adhd?
Well, as for how successful Lumosity is in working for adhd, I think it's a very good way to refresh and maintain working memory, which is important to ADHD sufferers.
However I would also say Brain Age and other software may be more cost-effective if you plan on doing this long term. They're not markedly better, but the alternatives are cheaper.
Overall, this kind of brain training is worth it though - whether with Luminosity or someone else, I think ADHD sufferers will benefit. Here's an interesting article if you're interested in understanding the science behind brain training and how it can help: http://www.sciencedaily.com/releases/2009/02/090206081507.htm