If they're willing to skip a kid up it might work out. The only thing I know about Saxon is that it is nearly impossible for a teacher to adapt it on the fly. As far as depth, I've heard varying opinions, but it seems possible to teach it very superficially, with an emphasis on rote learning and no understanding... and equally possible that a good teacher would do it much better. With no personal experience I can't really say with certainty one way or the other on that one.

Erica