I recently bought this kit and it was very nice.
The mesh numbers refer to the size of holes on the canvas. While my kit came with the 3.75 mesh canvas, I always prefer to use the 3.3 mesh canvas as it gives a much nicer finished product with a fuller look because the holes are smaller. I am still confused by the 5 mesh - I don't know if the holes are larger or smaller I assumed the larger the number, the larger the mesh, but I don't know for sure.
Happy Hooking!