Every fuelgun will leak a bit....
Take 2 same tanks, get an Xceed gun and a RB gun, fill them up and fill the tanks simultaneously, the RB gun is realy quicker and the end result is that the RB will fill it up to the edge and the Xceed not which can cost you drivetime up to one lap (with a 75cc tank).
The Losi has all the advantages of the RB and not the disadvantages.
But hey, these are just real experiences from just some drivers who just finally ended up with the Losi gun as best option.
Speed is only fiction but a 130+km/h MRS4 is for real.