Blade polishing can be fraught with problems, as S92mech stated: have a look at the MM before contemplating, let alone starting, any blade polishing. A lot of manufacturers place restrictions on what can and can't be used on main rotor blades. I had a set of LongRanger blades polished with a proprietary teflon polish, but only after it went through an approval process: well worth it, it put 9kias on the cruise speed
The BK117 is very sensitive to dirty blades: if it ever feels rough, or in need of a track and balance, a good wash of the MRB's will very often smooth everything out again. A lot cheaper than a T&B, too
We use CarbonX to clean the tail rotor blades on the 206's, very efficient and easy to apply, gets all the grime and soot off.