UC and 105, while using the same abrasive technology, couldnt be more different as far as they way they work. 105 is much more aggressive, but also much more difficult to use. It has a learning curve, and even with that it still is not easy. It has a very short working cycle and is hard to remove. UC on the other hand, not as aggressive, but easy to use as its a consumer focused product rather than professional. Long working cycle and easy to use. Also inexpensive and available everywhere.
In my experience, if an aggressive compound that is easy to use but also finishes well, check out Wolfgang Uber. Its one of my favorites. M105 has sort of been a measure by which other compounds cut is measured by, but its difficulty of use has it not on the top of many lists anymore.