I recently added a DE (Merkur Classic 1904 from Lynn and his crew @ SRD) to my rotation. I like having the option of using that or one of my straights, also there's days when I want a SR-like shave, but don't have the time. The DE fits the bill very nicely. As for using a modern (ie Mach3), I still have one in my gym bag, as I just can't see stropping my Rodgers 5/8 square tip in the locker room.