There’s nothing wrong with using a chisel and mallet for cutting door hinge mortises, but a trim router sure makes the job fast. I use a 1/4″ straight bit inside a standard guide collar for this task.
With this setup, hinge mortising becomes a standard template routing operation. I make a U-shaped template from scrap and fasten it to a base that I can clamp against the door frame. The template opening is sized to match the hinge leaf proportions, plus the amount of offset between the outer rim of the guide collar and the bit’s cutting edges. The template not only creates one uniform mortise after the next so you can cut them production style; it also creates a larger platform to help steady the router. The process is downright foolproof.
A number of trim router models come with bases that take guide collars; if yours doesn’t, you can usually buy an accessory sub-base that will. Or buy a universal sub-base for larger routers, cut it to size and screw it to your machine.