You can't grind them in a regular wheat type grinder. It takes a good corn type because the seeds are almost like stones. I have a wheat grinder that would break if I tried doing mesquite pods. I also have a huge old heavy Porkert that eats em up.
They're good. They don't spike diabetics sugars like other flours and they have a slight taste of honey. Need to inspect them for beetles though. (Not John, Paul, Ringo and George for you wise guys)
There are co-ops that have "Mill Days" just for grinding pods. Check with your county extension if you live in an area that has many mesquite trees like we do here in Arizona..