My QOV group uses a die cutter to make kits for us to sew and I HATE sewing them. I get much better results with shapes I have cut myself. The kit blocks are never square, they have jagged edges, and they don't lay flat. I hadn't thought of the grain and I'm glad you mentioned it UFO's Galore; that may be why I don't like the results when I use their kits. Next time I am at group I will look carefully at the pieces and see how true to grain they are. Bottom line is I have no interest in owning a die cutter.
ETA: I use Creative Grids rulers and Deb Tucker tools.