Professional Steel Brick Jointing Tool, 1/2" x 5/8", Dual-Ended Curved Blade for Masonry Filling and Sealing,Christmas Gift (1/2 x 5/8)

If you've made sure the stones don't explode and the mortar doesn't explode I would assume a metal lath is purely aesthetic. I would recommend using a grout smoothing tool like this one because it looks terrible right now.