I had looked on Dalla Columbina internet shop in italy better details with some info! no discription if latex is a progressive or extreme.,I could assume the c4 is alike the rob allan latex,.I Found seac power green was a progressive until they took it out of production then i got the sighal extreme free from a friend ! I found out that seac made a progressive although dipped in blue,.My friend said that with a double sling on a aluminium gun gave a kick back on the handle from the sighal 14mm extrem.I mounted on my own made padack gun with out the kick back when fired.Although i prefer the progressive i add 20cm for to compensate on the tension .,giving a longer life span on the period use of the latex.I found i got more Seabass even with the progessive speed i found id had the Seabass some times speared in the nose to tail ready for a barbeq.the countless times when the Seabass arrived for that second seing only the frontal then next second gone in a mirky water.I remember purchasing the omer latex black the standard gum false economy,.Then thanks to the progressive i felt alike a week end champion as all spear fishermen should