Mixing isn't going to 'hurt' anything since they all claim compatibility with all other oils. However, it's probably better to find one that works best for your vehicle(s) and go with it for best possible results. These oil companies research into formulas for good results. Of course, we are well aware that from time to time they must tweak their additive packages a bit to remain competitive in performance. Therefore it's probably good to find a brand that works well for your application and go with it. Now, there are people who are exceptions. There are a very few people on this board that I would trust in mixing, but they could be counted on the fingers on one hand with remaining digits.