Old Man Dave said:
You are right - thank goodness that there is no single answer and trust a Jerseyman to have a different perspective. I have owned pneumatic guns but can't get on with them. They seem to be overpriced and pretty clumsy looking but that is just a personal view. I know guys who swear by them and do very well. Each to their own.
A lot of Brittany spearfishermen use MATC tridents (on band guns) for bass, in holes and free swimming. These have wire barbs. I like to use a trident when I expect to see fish at short range and when I won't have time to aim for ages before pulling the trigger. I use a roller gun which is 75cm based on an Imersion speargun but heavily modified and as powerful at least as a 90cm gun. Although the spear is bulkier, the gun is shorter so it can be more discreet if you are hiding in kelp etc.
Good points for tridents are that they hit a fish so hard that if you hit the head of a good fish from close range then the actual impact can subdue the fish and recovering it is far easier than if the spear goes straight through and the fish ends up on the line. Japanese seaweed beds are a good example of the type of ground where this can be very useful although the tradeoff is that you cannot shoot through weed easily.
Also you can fish in far murkier water than you would with a straight gun and this can be very productive, as well as extending your season. How often do we get viz less than 3 metres in the CI?
The downsides are that you have to be patient and aware that long shots will not be successful. If you are the type of spearo who only hunts in 10m viz or wants to fire at everything you see or shoot very small fish or who doesn't worry about losing fish then its probably not for you. My personal preference is to keep calm and only take shots that are guaranteed. You can always have a straight gun on your buoy and alternate between the two to suit the conditions. Once you know an area you will be able to tell when to switch between the two.
One thing for sure is that you really need a trident like an MATC with long enough prongs to pass through the fish. Head on shots can result in difficulty getting the trident out and you need to be careful to keep the prongs straight. Clearly you cannot push the spear though as you can with a straight spear.
The Omer guns look great but personally I have always liked the articulated handles on Imersion guns as I find them less tiring.
Sorry if this is long winded, but I do like tridents.....