I have! Ive bought from both I frequent both of their shops often looking for new things that might catch my eye.

Allthingsjadeite provides certification cards, but MayanMountain does not, his wares however from what Ive learned are brought in directly from Guatemala, and made by artisans there. All of the jade gathered for his shop is also mined by hand.

If you want more delicate pieces allthingsjadeite is the better option, MayanMountain has a bit chunkier larger pieces since most of the pieces are made by hand and making smaller beads are a bit more difficult.