It's a good question to ask, but it's worth noting that there is no route that guarantees you a place on a DClinPsy. Any MSc, including the one you mention, will be a single part of a much larger portfolio of clinical experience, academic achievement and other skills you will have to pick up before you apply for training.
If you are of the belief that the MSc would be 'wasted' if you never got onto a DClinPsy, and it's going to create severe financial strain for you or your family, then I probably wouldn't risk it. It's currently a 15% acceptance rate which means 85% of applicants (most of whom have some postgrad qualificaiton or training) don't get on. However, if you were thinking of doing an MSc anyway, are passionate about the subject, and was willing to be quite flexible about the potential avenues that it may lead to then defintely consider it.