I would not recommend taking the MCAT in January during the program. They do not over-exaggerate the difficulty of the program, and it was much more difficult than anything I had ever done in undergrad. Only around 10 of us were able to meet the GPA requirement for the linkage, and half of the class did not make it to the spring semester. If I remember correctly, a few of my friends intended on taking the MCAT in around January at the beginning of the year, but they all pushed it to the summer and will be applying this upcoming cycle.
Of my classmates who applied this cycle, only 3 out of 8 of us used the linkage. The people who did not use the linkage had all taken the mcat prior to the program. Since I just graduated, I don't have personal experience with this, but I believe Mercer has a pretty good record of accepting alumni of the program the the Med school.