Using the same metal for both the grid and the foil improves the quality of your data because it reduces beam-induced motion caused by changes in the geometry and tension of the foil due to the elimination of the differential thermal contraction between grid and metal during plunge vitrification and sample irradiation. As discussed in Russo and Passmore, Science 346: 1377-1380 (2014) and Russo and Passmore. J. Struct. Biol. 193: 33-44 (2016).