You can make them as small or large as you want. I think Russia's Avangard glide vehicle should also be pretty large given the required launcher.
You can put a pretty huge unitary thermonuclear warhead on a glide vehicle like this one the North Koreans made I think.
This should make it easier for North Korea to bypass missile defenses in the region like AEGIS, AEGIS Ashore, or THAAD.
Russia has a similar missile program. The RS-26 Rubezh. But the program development has been frozen. Supposed to use a Yars derived first stage with a glide vehicle and to be launched from mobile launchers. Such weapon systems are basically banned by the INF Treaty. But the US left the INF Treaty to develop weapon systems like the Dark Eagle.