Distraction can be dangerous behind the wheel or cleaning a wheel.

Yes, it is definitely easier with the wheel off the bike and the rotor off the wheel. I had my wheel off to replace the tire so it was a no brainer to remove the rotor and clean the wheel.
 
I used Meguiars Wheel Brightener. I have been using this product for years without an issue. As long as you wash it off within a minute or two it works fine. I just left it on too long and it etched into the surface.
NONE of that stuuff is good for the finish our wheels are a machined finish and if the wheel is coated thats another issue
 
The best I've found is California Custom Aluminum Deoxidizer (Step 1) then Purple Polish by the same. It is easy, quick, and effective and very little abrasive.