I was just in Grand Rapids and they have a cool bike system. The bikes all have locks that are keyed to an app. To open a lock, they need your credit card. It's a dollar a ride (50 cents for students) and $14/week if you want to keep the bike overnight.
I think "free" is usually a bad idea for most things. There are exceptions obviously (Linux, Wordpress, etc; Seth Godin's first book, etc).
If you give away a really good book, everyone will take it and nobody will read it. If you charge $4.95 or $9.95, a lot fewer people will take it, but they will feel some engagement and actually read it.
Not that I've fully tested this, but I do have a book that I have made freely available for 20 years and as recently as a month ago I had three people ask me to "publish" it to make it "available" - until it costs money, it just isn't real to them.