My own experience has been 50/50.
Some testers are really good and they really like getting deep into the system, learning its intricacies and some are very confortable with code, yet they prefer testing instead of development. These testers show you things of your application that surprise you, and even seem to know the system under test better than you.
But others are really stubborn and seem to want to use the latest fad they learned in the latest testing conference. I discovered that the ones that tend to be bad are the ones that follow three prominent consultants of manual testing: Rex Black, James Bach and Michael Bolton, who really play down all forms of automation, especially BDD.