Whilst greatly improved one the 300 & 310. the 250 & 260's had a much higher fuel pickup, meaning you would run of of fuel available to the pump, yet still have fuel in the tank.
On the 300 and 310's the fuel pickup is lower, but again, still don't get access to all the fuel.
These R& D fuel extenders fix that. Limited quantity as R&D have closed down. Once sold, they are sold.