Again, I think that saying this is a bit much. There are a lot of Tau worlds, they won't be the exact same. Much like the Imperium. One Tau governor may be particularly harsh, and sterilise people for minor crimes, or if their family commits crimes (Criminality is, of course, an inherited attribute), or they may rely more on brainwashing education. It may depend. Another Tau governor may let the human planet do whatever it likes, so long as they give them crops or something.

Some will be progressive, others regressive. Mostly regressive though. I don't want to paint them as happy nice dudes.

Yes, they sterilise the population. Yes, they are Big Brother. However, this may vary in flavour from world to world. Just like the Imperium.

Also, nitpick. Arbites don't punish folk for murder. That's out of their jurisdiction and a heresy. ;)

Mentioning Arbites, though, is a good point. They are fairly consistent planet to planet. The punishments for not tithing to the Imperium are quite consistent, and the Arbites ensure that planets tithe required troops, supplies and unsanctioned psykers to the Imperium. They also take a hand in dealing with heresy and anti-Imperial sedition.

Punishments for lower level crimes, like murder and theft will vary widely depending on local traditions.

I imagine the Tau would be similar. On one planet they may allow local traditions, as part of social experimentation, not due to any respect for their subjects. They would likely treat social sciences as something similar to hard science, getting quite cold and creepy at times.

"Hmm, how effective will 80% tax compare to 60%? Try each on two different Hives. Keep it secret, so they do not know they are test subjects."

"Do public executions prevent murder more than sterilisation? We can consult case studies from the following planets..."