You can toast many different types of bread at the same time, but if you want your toast to be evenly brown, the bread must be of equal freshness. If one slice is drier than another, it will toast more quickly than the other and may even burn.
Avoid inserting slices that are too thick, and flatten the French baguette before inserting (both the inside of the bread and the crust side should not touch the heating elements). Also, do not warm bread or pastries on top of the toaster, as the fat in them could burn and may eventually damage the stainless steel.