Yup, I've used the Charity Miles apps on my Android and iPhone for more than a year. It's legit.
Sponsors kick in per mile in exchange for publicity. I post my rides to Facebook. The app tags the sponsors names onto my posts. That's all there is to it. No tricks. No spam.
My charity of choice is for Alzheimer's. My mom struggled with it for more than a decade before dying last month. Her older brother developed Parkinson's and dementia. Anything that helps research into the general field of dementia has my support.
And I use Amazon Smile, which kicks in some change from each eligible purchase toward Cook Children's Hospital, also near and dear. Cook saved my little cousin. He had open heart surgery in his first week of life, and subsequent surgeries over the years as he grew.
He's 13 now and you'd never know unless you saw his bare chest and what he calls his "zipper."
Between Medicaid and Cook benefactors his parents weren't saddled with a medical bill that almost certainly is approaching a million dollars.
I'd also suggest St. Jude's, Shriners, etc.