First and most importantly, fuel cleaning service is not on Mazda's maintenance schedule.
These are things that dealers "believe" you should spend $$$ to do.
Of course, we should not spend money on whatever dealers say. We do whatever Mazda says
for the sake of warranty. Now that if your CX9 is out of warranty, you do whatever you see fit.
Unless you detect issues in fuel system, I don't think service like this is necessary at all.
For me, I dump a bottle of Gas Treatment ($1 each) on every other tank into the gas tank.
That should take care of it (the fuel system) and keep it clean.