Agreed that there is no type rating for a Twin Otter.
However, Flight Safety's Twin Otter simulator is fantastic to fly, and will allow you to things which you would be crazy (or fired) for trying in the real thing! I flew it about 40 hours in the late '90's, mostly single pilot and gained a lot of confidence in it, and multi engine flying in general.
That said, I agree with those who write to you that it may not be the best investment at this stage. Save your money for a while, get a job, and then offer to match funds with your employer if they'll send you on the course.
You will learn more, if you've been "out there" for a while, and have built up the experience to have some good questions during the training. Otherwise, part of your expensive training dollar will go unappreciated.
Cheers, Pilot DAR