Every time I've ever taken a run at adding locations to RM I run into the issue of it only works for GMs who are fine with on the fly changes like when you get:
"Blow to side of head, lose use of one eye due to swelling for 24 hours -50 to all actions, stunned no parry for 1 round."
But the strike was to the leg, so the GM has to change it on the fly into:
"Blow to thigh, lose use of one leg due to deep bruise for 24 hours, -50 to all actions, stunned no parry for 1 round."
It'd be tempting to say make the crit generic ala:
"Blow causes a temporary loss of function to the area struck, -50 to all actions, stunned no parry for 1 round."
But, while that would make the GM call more obvious, the GM would still have to decide "Eye, nose, ear, mouth, hmm" for a head shot, or "Leg, foot, knee, hip, thigh, shin, toe, hmm." with a leg shot so there would still be just as much work to do. . .
And such generic criticals would be kinda bleh. . .I like the gory, amusing criticals. . .but for gory and amusing you need details.