I wouldn't sweat the grease groove design. I've used both keith style, and LBT shallow rounded grooves, I haven't seen any difference.
As far as mold materials, I really like cast iron and steel molds, ballisticast being my favorite, but they are pricey. I have a buddies Mountain mold that is brass, and it casts ok. I've only cast two brass molds, this one and an applegate, and I've found them to be the most finicky mold material, there seems to be a narrow band of mold temperature that results in good bullets, not too hot, and not too cool. I've never had a problem with aluminum molds, I've used NEI, LBT, Hock and I have a handfull of lee molds.
The only thing I don't like about MM, is the aluminum sprue plate. Other then that, he offers a good custom mold at a fair price, but I'd save the $ and get it in aluminum.