it is the mechanism that is so much better. If you are getting the BYU buckle at Mission Belt, probably just buy the whole belt there. I might still get their all white version for my white temple clothes. They are still a good product, I just like the SlideBelt mechanism a ton better.
Check out the story line here to see the difference -
https://www.slidebelts.com/pages/our-story
Mission Belt look much like the 2008 version of the SlideBelt. The SlideBelt guy actually used some version he saw on his mission in Europe to create the design and won some prize while at BYU. That is what his cousin took to the Shark Tank. The 2012 version was a total redesign and the mechanism is triggered by pulling forward on the outer ring of the belt rather than a little switch on the bottom. I found that switch jammed a number of times and was hard to trigger on some of the belts I bought.
The SlideBelt mechanism is smooth to operate and I think has a much cleaner and professional look to it.