A lot depends on influence of hitting instructor. My kid does indeed have a downward swing and finishes with a "smile". HS coaches teach same method. Works for him as he's always finished at or near top of BA, slugging %, RBI's etc. Don't think a kid can hear "swing down" on ball & work unless he fully understands & properly taught method. As far as long toss from knees; obviously worked for Kimbrel. Don't think I'd tell my kid to do it before knowing a little more about it though. By same token; not going to dismiss as wrong.