I have one! She's tough as nails, you can shoot blanks over her head, have a stranger charge her, whatever... solid as a rock. But if I so much as whisper a 'no' she is flat on the ground and acts like she was just flogged. That's useful in the sense that she will recall out of ANYTHING and I never have to worry about compliance but it does make training difficult. She gets frustrated easily when she perceives she's not pleasing me. If she's not offering the behavior I'm looking for she's not very teflon or persistent, she just shuts down and starts soliciting or apologizing (offering her belly, whining etc) instead of shrugging it off and trying again. I've never had to use any sort of training collar with her. The most 'harsh' correction I've ever had to give her is a raised voice. The trick with her has been short sessions and very slow shaping. Marker training has worked superbly with her, as does training with other dogs. One-on-one seems to be a lot of pressure. She knows it's a 'session' and is easier to accidentally shut her down. If she's in a group she shrugs off a failed response and tries again instead. Once she understands a cue she's johnny-on-the-spot; instant response, flawless execution. The trick is just building her confidence.
I just edited to add that when I hand her off to someone else she's stubborn as a mule... it's hilarious. They can drag her all over kingdom come and she'll just ignore them. It's not necessarily a soft dog, just very handler respectful.