I suppose it does depend how commited you are to a career as an Officer, it might be a good idea to join the OTC and make your decision whilst not in receipt of the bursary. If you like what you see and hear then go for it, that is if the Chancellor has any cash left to give away!
I agree with pimpernel. Join up with the OTC in your first year and experience what its like, then if you decide to go for it. You can apply for the bursary after your first year and recieve it for the remaining years of your course.