1. Marathon has the US military contract. The others don't 2. The bezel on the Marathon is taller so you can grab it with gloves on 3. The level of lume on the Marathon isn't the brightest so you can see it without getting shot by the enemy. 4. A bidirectional bezel is bad because if you are diving and you end up rubbing it against something, it can tell you that you have more time/air in your tanks that you actually have. Unidirectional bezels could only ever tell you you have less air than you have, which means you won't stay underwater and run out of air so long as you set it properly.
1. Marathon has the US military contract. The others don't
2. The bezel on the Marathon is taller so you can grab it with gloves on
3. The level of lume on the Marathon isn't the brightest so you can see it without getting shot by the enemy.
4. A bidirectional bezel is bad because if you are diving and you end up rubbing it against something, it can tell you that you have more time/air in your tanks that you actually have. Unidirectional bezels could only ever tell you you have less air than you have, which means you won't stay underwater and run out of air so long as you set it properly.