Mixing the two is very useful. I typically make headers and footers with flex, build home page grids with grid, and then use flex to space out content in the ce

Mixing the two is very useful. I typically make headers and footers with flex, build home page grids with grid, and then use flex to space out content in the cells. No more floats, no more percent widths, no more weird nth child tweaks for positioning. Add rems to the mix and responsive design has never been simpler. For grids you can just change from say a 3 column grid to a single column on mobile for most cases. And the best part, no bootstrap.