Box trainers provide realistic ‘haptic feedback’ (the sensation and resistance of actual tissue) but do not provide an objective assessment of skills. VR simulators do give an objective assessment but lack the realistic haptic feedback.
Augmented Reality is a new form of simulation, in which physical realism is combined with VR. Realistic haptic feedback is provided by the fact that the surgeon practises using real materials and instruments, and objective assessment is also possible because the position of the instruments can be determined. (source)
Unfortunately, it's hard to tell from the press release what exactly did Botden change in the ProMIS simulator. Browsing through ProMIS's site, it seems that it was previously designed to use AR as a method for training for surgeries, even laparoscopies. See for example the following video (some virtual blood is involved), where the simulator guides the trainee through the procedure. Nevertheless, ProMIS seems like a very cool device, and I can only wonder what are type of precisions involved tasks can be learned using AR.