I just got done with the Osler in Tampa (actually I am in Tampa right now). The Osler course isn't perfect, but it does allow some focus on the subject and time away from home/work.
Honestly I thought that it would be better than it was, mainly in the radiology review. Also, one of the neuro-oto lecturers was highly unorganized and fiercely opinionated. For example: when asked, "Tell us about rotary chair and optokinetics, he replied, 'You don't need to know any of that, it is irrelevant.'"
My thoughts: no course will prepare you for the minutia of the written boards. Residency will prepare you pretty well, and then look to KJ Lee, Pasha, or Pearls to polish up for before the test. The Osler may fill in some gaps, and can certainly help with the orals, giving you high yield info. Beyond that, don't think that just taking Osler will make you pass, as it has no lectures on sinus/allergy/OSA/anesthesia and many other general oto topics.
Actually, I would be pretty upset if the tab were on me ($1390 for the week, plus hotel and flight costs...over $2K), considering how poor the radiology and some of the neuro-oto lectures were. That said, I am glad that I took it (on the company tab) and got away from work. The facial plastics and H&N were particularly good.
I will caveat this by saying that if I pass, I may come back to this forum in the late spring/summer and heartily endorse the course. If i fail, well, you might hear about some oto in Arlington, TX having a nervous breakdown.
In summary, if you are really worried about passing, spend the cash to take the course. It can't hurt, and hanging out with your fellow otos is fun in a "camp" sort of way.