It is hard for me to imagine that the process of cutting a mitred rabbet joint could be faster than a domino mortising. If you are familiar with the domino mitreing, there can be zero test cuts. It is almost impossible that you can set the saw fence right without test cuts.
Strength-wise, it is an end-grain to end-grain, and long/face-grain to long/face-grain glue-up in a domino mitre, while the mitred rabbet is an end-grain to end-grain, and end-grain to long/face-grain glue-up. So I would say the domino mitre is stronger.
One additional benefit of using the domino joiner ... dust free.