I've used it for years and have never seen any dirt in the air boot or intake tract on my bikes. We ride in some seriously hot dusty conditions in the summer, and it oil has never had problems staying on the filter and doing it's job. It seems to be as good as anything else when the going gets muddy as well.
I found it very easy with this oil to get the filter properly coated without running into issues with over-oiling and clogging the small passageways on the FCR carbs.
I don't know that the K&Nis any better than any other oil but I haven't seen anything over the last 5 years that would make me think it's any worse than Twin Air oil. Twin Air IMO is an excellent oil but much more work to deal with.