There's a competition-level BMX track down the street from me, and a pump track down the street the other way. However, I don't have a mountain bike or BMX bike so I don't use them. When I was a teen, I rode BMX quite a bit. It's great for bike handling skills. I think it could only help your mountain biking skills.

My brother, who is an excellent MTB rider and BMX rider, regularly rides on a pump track. He and his neighbor built one in the neighbors yard. It's really good for core strength.