Advantage:
You get into med school EARLY. This means:
-No MCAT
-Save $$$ on applications
-No feeling like you have to spend your time doing x, y, z to get into med school
-therefore you can spend the rest of college doing whatever you want
-You can be relaxed knowing you already know what you're doing!
-Reap your last possible reward for doing well in high school and on the SAT
This is all provided that as soon as you get in your grades don't drop.
Such programs are competitive, because they want to accept people that they are sure will do well in medical school. Basically by the time you're a sophomore your grades and experiences should be comparable (if not better) to a typical applicant who would be accepted as a senior.
With that said, much fewer students apply to early programs so in terms of percentages, the acceptance rate could quite possibly be higher for early acceptance programs. Then again, the students who apply are self-selecting and will probably have higher stats than your average pre-med.