I service and own several different Mares regs. As far as bubble dispersion, it is pretty tough to beat a large exhaust tee such as found on some of the older models like the Akros or Nikos. My Proton Metal second stages seem to be a bit better than the polymer bodied Proton, but this would be a minor difference.
While swimming forward in a horizontal position, I hardly notice any bubbles from either Proton design. If vertical, then I do notice a few obscuring my vision; particularly if not moving forward much.
I absolutely love tuning the Proton regs. They are so simple to adjust due to the side port. I adjust the primary second stages to have a cracking effort of 1.2", and that is just about perfect for their case geometry fault design. While in the normal swimming position, they have very little cracking effort.
When you consider the rugged simplicity of their second stages, and the fact that they easily meet the US Navy "Class A" standards, they are an outstanding choice.
Greg Barlow