The RG-2100S is a non-adjustable 2nd stage, suitable for either a primary or secondary 2nd stage.  The front cover of the 2nd stage is user changeable and available in 6 different colors (Green, Blue, Purple, Orange, Red, Yellow). 

The RG-2100S comes supplied with a 75cm (29 inches)...

The RG-3100S is an adjustable 2nd stage, the pneumatically balanced design gives consistent gas flow at all times.  Featuring a Venturi assist to produce a smooth inhalation, and a dive/pre dive lever to help avoid free flows on the surface. 

The adjustable design allows the diver to...