They call it Dual Enrollment in California. It has been around for decades. It was free when I was in High School, but all Community College classes were free in California prior to the passage of Prop 13 in 1978.
Not sure if it is free anymore.
IMHO that is a great option for students, the tougher the classes that they take, the better. However, be prepared, depending on the College your child chooses after High School, the credits may not be accepted. Some colleges want you to take THEIR version of the class. But clearly if a student has already taken someone's version of a class, I would think they would be bound to do better in another college's version.
In Minnesota the Community College presents you with a list as part of acceptance telling you which classes will move over to meet what general ed requirements at Minnesota public colleges. Since most of the kids in Minnesota doing PSEO to save money will move to a Minnesota public four year, there isn't a lot of excuse for "it won't transfer." Out of State schools or private schools might not accept the credits, but at the point at which you are sending kids outstate (Minnesota doesn't have great reciprocity programs) or private, money is no longer your first concern. Most Minnesota private schools are very familiar with PSEO and will accept the credits - although perhaps not credits in your major.