I have always been told that the changing of partners is a good thing. Firstly each person that we pratice with will attack slightly different, they will have different size limbs, different pain thresh holds, different body reactions & therefore we need to learn how to make the minor adjustments to each techinque, when we apply them, so they will work properly. Secondly training with people from different levels is a good because, those of a higher grade can teach you from their experience. Those from a lower grade teach you because you have to think about what you are explaining to them & they sometimes react unexpectedly. While you learn from those of the same level, because it's a kind of experimental workshop where you help each other. Plus when you train with people from other styles, they often have a different view on how a technique should be done.
Personnel I like to learn by feeling the technique, in the uk I have two sensei's, when both do shironage one sensei feels like he is about to ripe my arm out of my socket then suddenly I am looking up from the mat. The other one feels very smooth, like nothing is happening, then suddenly again I am looking up from the mat. Recently I've been studying with another sensei and again shironage is completely different with much more emphasis on the wrist lock. All three are valid ways to perform the same technique & all three finish the with uke look up from the mat. As the saying goes "There is more than one way to skin a cat"