The only negative thing I've come across using Medlink is that they are very keen to get you on the ground to investigate further. This may sound sensible most of the time, but that little nerdy accountant part of the pilots brain starts to ring up the dollar signs, and you know that you are talking to medics, not ops.
Having said that, if a doc says to me 'you need to land' then I can stand quite happily in front of my boss when I have to explain why I diverted at vast expense to the company, because I have done the right thing.
Not sure if this answers your point, but it might show a different light on the subject for you.