Seriously, the vast majority of the comments clearly have no clue as to what the device is, or how it works. Everyone seems to be thinking of tech they read about decades ago. First up, look at the name of the technology. "Digital radio frequency memory". There is a clue here.
Radar works by the missile sending a pulse out, and listening to the return. In modern systems that pulse shape can be very smart, and radars can see a lot about the target from the pulse return. Not just signal strength, but doppler shift and a host of second order clues. The point of a DRFM system is to spoof the missiles radar, knowing that this is the sort of thing it is going to be trying to do. So how? In principle it is easy. Receive the pulse, record it (the "memory" bit of the name) slam it into a custom bit of seriously fast custom silicon or FPGA, and work out what the return pulse needs to look like to make the missile think what you would like it to. It isn't necessarily a matter of making the can look like your plane directly. The can can spoof the doppler profile expected from your plane. Even if the missile changes its pulse profile, the DFRM system will continue to work, as it records and replays each pulse as needed. This is not your grandmother's radar jammer.
As to optical missile and guidance systems. Active laser systems are already available with the ability to blind incoming missiles. There will always be a mix of radio and optical threats, the presence of one does not mean you discard managing the other.
It is exactly an arms race. Missiles can have upgraded software to try to work past DFRM systems, and those same DFRM systems can have upgraded software to cope with that.