A couple of things..
At Tufts, we are never graded against each other; we are graded against the medical school students. BUT, since the top 25% are guaranteed interviews, it is essentially as if you are being graded against each other.
On that note, since the program here is relatively new, there aren't any "hard" statistics regarding the % of interviews offered or % of students matriculating into medical school. However, the Dean of the medical school has said that they estimate they have invited more than 50% of MBS students for an interview. I have also noticed that almost all of our TAs were in the MBS program last year, which is a significant proportion of the M'14 class.
As for "getting in trouble" for attending the medical school lectures and the lectures not being med school equivalents, that's a crock of

. First off, I went to maybe 3 lectures with the MBS students, and in the 50+ lectures I attended with the medical students, I have never heard anyone complain. The medical students were actually friendly and held conversations with me.
In terms of med school equivalents, the content in the MBS lectures are literally the same as in the medical school lectures. Here's where the difference arises:
1. As gujudoc said, Tufts' curriculum is systems-based. Therefore, the med students have their CV block, where they learn all the physiology/pathology/anatomy of the CV system, and the respiratory block, etc. Essentially, you can think of the med students as having a bunch of courses, each focusing on a body system. The MBS students, on the other hand, take physiology, pathology, and anatomy. Usually, the 3 courses attempt to cover the same body systems at the same time, but they don't always align. Thus, you can think of the MBS students as having a bunch of courses, each focusing on an aspect of the body (the physiology of the body, the pathology of the body) instead of covering everything about one body system.
2. The med curriculum goes WAY more in depth (which is expected since the CV block, for example, occurs in the 2nd year of med school and is all the students learn about for several weeks/months). But, if you took the first 5 physiology lectures of the CV block, the respiratory block, etc., and combined them all together, you would get the MBS physiology course.
3. The above ONLY applies to 2nd semester. 1st semester is literally identical to the medical students (with the exception of the last 3 weeks where MBS students have Intro to Clinical Medicine & pharmacology instead of pharmacology + beginning systems blocks).
I don't know anything about BU other than what I've read in this forum, so I am not drawing comparisons here...I am just trying to describe how the Tufts program works. It's ultimately up to each person to decide which aspects of whatever program they prefer, so they can determine which program is the better fit.
In that respect, I think other people in this forum need to do the same -- talk about what you know and not what you think your friends know.