Ryan has a lot of great points.
When I used M105 for the first time, I thought it was pretty aggressive and had a super short working time. Now that I have mastered how the product works, I can work it for several minutes at slower speeds on a foam pad.
On some paints (usually soft), it works incredibly well, but on others, not so well. I consider it more of a medium grade polish instead of an aggressive compound. Sometimes it really surprises me on harder clears though.
I think that many people aren’t working the product long enough because they can’t physically see the product on the surface. If you look carefully while polishing with M105, you will see a slight film on the panel which can be worked until it turns into a very fine powder, similar to baby powder.
3M Extra Cut (06060) is one of my favorite compounds on harder paints, although it doesn’t finish off as nice as 105. The finish left after compounding doesn’t really matter to me. What really matters to me is that the defects are fully removed. Compounding haze left from 3M EC is easily removed with a medium grade polish, as suggested by 3M and finished off with a finishing polish. I think too many people are forgetting that it is a compound, not a medium or finishing polish.
I think the only way to get a perfect finish is to 3-step a car at minimum (compound, medium polish & final polish). Sometimes I find that as many as 6 or 8 stages are necessary for me to get the results I am happy with. Once in a while you will get lucky and get away with doing a 2-step, but almost never.
Both M105 and 3m Extra Cut are great products and have their place in my product arsenal. Are they the only 2 compounds I have? Absolutely not! You can never have too many products on hand for when you run into problems, which is why I am always trying new products, pads, techniques, etc… Like Ryan stated, there is no one fix for all paint. Problem solving is part of being a professional detailer. If there was one product that worked on all paint, everyone would be a professional!