I've also had the Mission Belt, which I bought after they were on Shark Tank.

The quality of this is so superior to the Mission Belt, it isn't even fair to compare them.  And I just checked: they are the same price. Here are the specifics:

Slidebelt, : pro: superior "whole buckle" flip opening; overall quality build (that just feels expensive).  Con: it is impossible to get the buckle off the belt at TSA pre-check.

Mission belt, pro: easier to take of the belt (which is what I do at TSA pre-check); nice mission story.  Con: Overall inferior build quality (that feels cheap, once you've had a Slidebelt); the tab on the bottom that opens the belt is sharp (and actually cut me once).