Much like Mao Pam's wings, demons can take on a wide variety of forms, create sensory organs, and are able to operate autonomously. Unlike her actual wings, manufactured demons are much weaker and unable to morph at will. Different "models" of demons exist with varying strength and intelligence. Demons are sought after as weapons and security measures, with the low-level, less intelligent demons being used as guards by Mages.
The following contains plot details/spoilers, read at your own discretion:
Before Magical Girl Raising Project
Long before Unmarked, an incident occurred during Cranberry's selection test, in which a Magical Girl with the ability to summon nearly anything summoned a powerful demon that went berserk and killed all the participants of the test except for Cranberry. The exact reasons for its summoning are unknown to the Land of Magic, but it's believed to have been caused by Fav.
Following this incident, the production and use of higher-level demons were outlawed within the Land of Magic and the powerful models were destroyed. Despite this, illegal models appear to continue to be produced.
Magical Girl Raising Project: JOKERS
During the events of JOKERS, the Pure Elements are instructed to travel to remote locations and fight demons there, known as Disruptors to them. They would collect the remains of the demons several days after fighting them, when they finally break down, and somehow reverse-engineer them to create new gadgets and powers.
Magical Girl Raising Project: ACES
In ACES, Princess Deluge commands a large number of high-level demons.