The main reason for adopting reverse triggers is that they are shallow and can allow the grip handle to sit higher up so that the spear axis is not far above your hand. The downside is that they only dry fire thanks to the weight of the sear lever arm as they usually have no biasing spring on that arm. Exceptions are the Sea Hornet and Biller which use a leaf spring to bias both levers, but that deepens the mechanism housing. If you want more band draw then you need a longer gun. It would be possible to bury a standard trigger in the speargun grip and fire it via a remote trigger from in front of the grip, much like a mid-handle gun using a short link or pushrod.
The sear lever pivot pin position with respect to the sear lever tooth determines how readily the sear lever rolls. On standard mechanisms it usually sits below and just behind the tooth, but on reverse mechanisms it can be found further back. This may tend to cause drag on the tooth as it tips through a smaller arc, unlike standard mechanisms where the sear lever tips through a much larger arc to let the shaft go.
The sear lever pivot pin position with respect to the sear lever tooth determines how readily the sear lever rolls. On standard mechanisms it usually sits below and just behind the tooth, but on reverse mechanisms it can be found further back. This may tend to cause drag on the tooth as it tips through a smaller arc, unlike standard mechanisms where the sear lever tips through a much larger arc to let the shaft go.